Led light bulb having filament with layered light conversion layer

ABSTRACT

An LED light bulb, comprising of: a lamp housing; a bulb base connected to the lamp housing; a stem connected to the bulb base and located in the lamp housing; a single flexible LED filament, disposed in the lamp housing, the flexible LED filament comprising: a plurality of LED sections; a plurality of conductive sections, located between the adjacent two LED sections, where each of the conductive sections includes a conductor, the conductor is copper foil; at least two conductive electrodes; and a light conversion layer comprising a phosphor layer and a silicon layer superposed on the phosphor layer, disposed on the LED chips and at least two sides of the conductive electrodes, and a portion of the conductive electrodes is exposed by the light conversion layer, the LED chip comprising a upper surface and a lower surface opposite to the upper surface of the LED chip, the phosphor layer directly contacts the upper surface of the LED chip, and a base layer contacts the lower surface of the LED chip; the base layer is formed from organosilicon-modified polyimide resin composition comprising an organosilicon-modified polyimide and a thermal curing agent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 16/479,220 filed on 2019 Jul. 19, which claims priority to ChinesePatent Applications No. 201711434993.3 filed on 2017 Dec. 26; No.201711477767.3 filed on 2017 Dec. 29; No. 201810031786.1 filed on 2018Jan. 12; No. 201810065369.9 filed on 2018 Jan. 23; No. 201810343825.1filed on 2018 Apr. 17; No. 201810344630.9 filed on 2018 Apr. 17; No.201810501350.4 filed on 2018 May 23; No. 201810498980.0 filed on 2018May 23; No. 201810573314.9 filed on 2018 Jun. 6; No. 201810836433.9filed on 2018 Jul. 26; No. 201810943054.X filed on 2018 Aug. 17; No.201811005536.7 filed on 2018 Aug. 30; No. 201811005145.5 filed on 2018Aug. 30; No. 201811079889.1 filed on 2018 Sep. 17; No. 201811277980.4filed on 2018 Oct. 30; No. 201811285657.1 filed on 2018 Oct. 31; No.201811378173.1 filed on 2018 Nov. 19; No. 201811378189.2 filed on 2018Nov. 19; No. 201811549205.X filed on 2018 Dec. 18, each of which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a lighting field, and moreparticularly to an LED light bulb having filament with layered lightconversion layer.

RELATED ART

Incandescent bulbs have been widely used for homes or commerciallighting for decades. However, incandescent bulbs are generally withlower efficiency in terms of energy application, and about 90% of energyinput can be converted into a heat form to dissipate. In addition,because the incandescent bulb has a very limited lifespan (about 1,000hours), it needs to be frequently replaced. These traditionalincandescent bulbs are gradually replaced by other more efficientlighting devices, such as fluorescent lights, high-intensity dischargelamps, light-emitting diodes (LEDs) lights and the like. In theseelectric lamps, the LED light lamp attracts widespread attention in itslighting technology. The LED light lamp has the advantages of longlifespan, small in size, environmental protection and the like,therefore the application of the LED light lamp continuously grows.

In recent years, LED light bulbs with LED filaments have been providedon the market. At present, LED light bulbs using LED filaments asillumination sources still have the following problems to be improved.

Firstly, an LED hard filament is provided with a substrate (for example,a glass substrate) and a plurality of LED chips disposed on thesubstrate. However, the illumination appearance of the LED light bulbsrelies on multiple combinations of the LED hard filaments to produce thebetter illumination appearances. The illumination appearance of thesingle LED hard filament cannot meet the general needs in the market. Atraditional incandescent light bulb is provided with a tungstenfilament, the uniform light emitting can be generated due to the naturalbendable property of the tungsten filament. In contrast, the LED hardfilament is difficult to achieve such uniform illumination appearances.There are many reasons why LED hard filaments are difficult to achievethe uniform illumination appearance. In addition to the aforementionedlower bendable property, one of the reasons is that the substrate blocksthe light emitted by the LED chip, and furthermore the light generatedby the LED chip is displayed similar to a point light source whichcauses the light showing concentrated illumination and with poorillumination uniformity. In other words, a uniform distribution of thelight emitted from LED chip produces a uniform illumination appearanceof the LED filament. On the other hand, the light ray distributionsimilar to a point light source may results in uneven and concentratedillumination.

Secondly, there is one kind of LED soft filament, which is similar tothe structure of the above-mentioned LED hard filament and is employed aflexible printed circuit substrate (hereinafter referred to FPC) insteadof the glass substrate to enable the LED filament having a certaindegree of bending. However, by utilizing the LED soft filament made ofthe FPC, the FPC has a thermal expansion coefficient different from thatof the silicon gel coated covering the LED soft filament, and thelong-term use causes the displacement or even degumming of the LEDchips. Moreover, the FPC may not beneficial to flexible adjustment ofthe process conditions and the like. Besides, during bending the LEDsoft filament it has a challenge in the stability of the metal wirebonded between LED chips. When the arrangement of the LED chips in theLED soft filament is dense, if the adjacent LED chips are connected bymeans of metal wire bonding, it is easy to cause the stress to beconcentrated on a specific part of the LED soft filament when the LEDsoft filament is bent, thereby the metal wire bonding between the LEDchips are damaged and even broken.

In addition, the LED filament is generally disposed inside the LED lightbulb, and in order to present the aesthetic appearance and also to makethe illumination of the LED filament more uniform and widespread, theLED filament is bent to exhibit a plurality of curves. Since the LEDchips are arranged in the LED filaments, and the LED chips arerelatively hard objects, it is difficult for the LED filaments to bebent into a desired shape. Moreover, the LED filament is also prone tocracks due to stress concentration during bending.

In order to increase the aesthetic appearance and make the illuminationappearance more uniform, an LED light bulb has a plurality of LEDfilaments, which are disposed with different placement or angles.However, since the plurality of LED filaments need to be installed in asingle LED light bulb, and these LED filaments need to be fixedindividually, the assembly process will be more complicated and theproduction cost will be increased.

Patent No. CN202252991U discloses the light lamp employing with aflexible PCB board instead of the aluminum heat dissipation component toimprove heat dissipation. Wherein, the phosphor is coated on the upperand lower sides of the LED chip or on the periphery thereof, and the LEDchip is fixed on the flexible PCB board and sealed by an insulatingadhesive. The insulating adhesive is epoxy resin, and the electrodes ofthe LED chip are connected to the circuitry on the flexible PCB board bygold wires. The flexible PCB board is transparent or translucent, andthe flexible PCB board is made by printing the circuitry on a polyimideor polyester film substrate. Patent No. CN105161608A discloses an LEDfilament light-emitting strip and a preparation method thereof. Whereinthe LED chips are disposed without overlapped, and the light-emittingsurfaces of the LED chips are correspondingly arranged, so that thelight emitting uniformity and heat dissipation is improved accordingly.Patent No. CN103939758A discloses that a transparent and thermallyconductive heat dissipation layer is formed between the interface of thecarrier and the LED chip for heat exchange with the LED chip. Accordingto the aforementioned patents, which respectively use a PCB board,adjust the chips arrangement or form a heat dissipation layer, the heatdissipation of the filament of the lamp can be improved to a certainextent correspondingly; however, the heat is easy to accumulate due tothe low efficiency in heat dissipation. The last one, Publication No.CN204289439U discloses an LED filament with omni-directional lightcomprising a substrate mixed with phosphors, at least one electrodedisposed on the substrate, at least one LED chip mounted on thesubstrate, and the encapsulant coated on the LED chip. The substrateformed by the silicone resin contained with phosphors eliminates thecost of glass or sapphire as a substrate, and the LED filament equippingwith this kind of substrate avoids the influence of glass or sapphire onthe light emitting of the LED chip. The 360-degree light emitting isrealized, and the illumination uniformity and the light efficiency aregreatly improved. However, due to the fact that the substrate is formedby silicon resin, the defect of poor heat resistance is a disadvantage.

SUMMARY

It is noted that the present disclosure includes one or more inventivesolutions currently claimed or not claimed, and in order to avoidconfusion between the illustration of these embodiments in thespecification, a number of possible inventive aspects herein may becollectively referred to “present/the invention.”

A number of embodiments are described herein with respect to “theinvention.” However, the word “the invention” is used merely to describecertain embodiments disclosed in this specification, whether or not inthe claims, is not a complete description of all possible embodiments.Some embodiments of various features or aspects described below as “theinvention” may be combined in various ways to form an LED light bulb ora portion thereof.

It is an object of the claimed invention to provide an LED filament, theLED filament comprises at least one LED chip, at least one pair ofconductive electrodes, a first light conversion layer, a Polyimide film(hereinafter referred to PI film) and a copper foil. The copper foil andthe LED chip are attached to the upper surface of the PI film, thecopper foil is located between two adjacent LED chips, and theconductive electrodes are disposed corresponding to the LED chipconfiguration. The LED chip and the copper foil, and the LED chip andthe conductive electrodes are electrically connected by at least oneconductive wire. The LED chip is provided with a p-junction and ann-junction, wherein the conductive wires comprise a first wire connectedto the p-junction of the LED chip and a second wire connected to then-junction of the LED chip, the first light conversion layer covers asingle LED chip and part of a first wire and a second wire which areconnected with the LED chip, the number of the first light conversionlayers is the same as the number of the LED chips.

In accordance with an embodiment with the present invention, a silverplating layer is arranged on the upper surface of the copper foil, and asolder mask layer is arranged on the silver plating layer, wherein thethickness of the solder mask layer is in a range of about 30 to 50micron (μm).

In accordance with an embodiment of the present invention, the firstlight conversion layer covers two ends of the copper foil, wherein thecovering area or the average thickness of the first conversion layerdisposing on each of the two ends of the copper foil are the same or notequal. The first light conversion layer covers the upper surface of thecopper foil with an area ratio about 30 to 40 percent.

In accordance with an embodiment of the present invention, the firstlight conversion layer covers the copper foil, wherein the covering areaor the average thickness of the first conversion layer disposing on thetwo ends of the copper foil and on the middle of the copper foil are thesame or not equal. The first light conversion layer covering the middlesurface of the copper foil has a thickness in a range of about 30 to 50micron (μm).

In accordance with an embodiment of the present invention, a pair ofconductive electrodes are respectively located at the ends, the head endand the tail end, of the LED filament and extending beyond the locationwhere the copper foil on the PI film.

In accordance with an embodiment of the present invention, a secondlight conversion layer is disposed under the PI film, and the secondlight conversion layer is provided with an inclined surface or aninclined surface with an arc shape, wherein the upper surface of the PIfilm opposites to the lower surface thereof.

In accordance with an embodiment of the present invention, the surfaceof the first light conversion layer is an arc shape, and the height ofthe arc shape gradually decreases from the middle to the both sides withrespect to the PI film, and the angle between each of the two sides ofthe curved shape and the PI film is an acute angle or an obtuse angle.

In accordance with an embodiment of the present invention, an LEDfilament comprises a plurality of LED chip units, a plurality ofconductors, and at least two conductive electrodes. Wherein each of theconductors is located between two adjacent LED chip units, the LED chipunits are disposed at different heights, and the conductive electrodesare disposed corresponding to the LED chip units configuration andelectrically connected to the LED chip unit by the wire. The adjacenttwo LED chip units are electrically connected to each other through aconductor, and the angle between the conductor and the extendingdirection of length of the LED filament is in a range of about 30° to120°. In accordance with another embodiment of the present inventionprovides a composition which is suitable for use as a filament substrateor a light conversion layer, wherein the composition comprises at leasta main material, a modifier and an additive. The main material is anorganosilicon-modified polyimide; the modifier is a thermal curingagent; and the additives comprise microparticles added into the mainmaterial, which may comprise phosphor particles, heat dispersingparticles. The additive also comprises a coupling agent.

The present disclosure provides a composition which is suitable for useas a filament substrate or a light-conversion layer, wherein the mainmaterial in the composition is an organosilicon-modified polyimide, i.e.a polyimide comprising a siloxane moiety, wherein theorganosilicon-modified polyimide comprises a repeating unit representedby general Formula (I):

In general Formula (I), Ar¹ is a tetra-valent organic group having abenzene ring or an alicyclic hydrocarbon structure, Ar² is a di-valentorganic group, R is each independently methyl or phenyl, and n is 1˜5.

According to an embodiment of the present disclosure, Ar¹ is atetra-valent organic group having a monocyclic alicyclic hydrocarbonstructure or a bridged-ring alicyclic hydrocarbon structure.

According to another embodiment of the present disclosure, Ar² is adi-valent organic group having a monocyclic alicyclic hydrocarbonstructure.

In accordance with an embodiment of the present invention, a perspectivediagram of the light emission spectrum of an LED light bulb is provided.The LED light bulb may be any LED light bulb disclosed in the previousembodiments, the spectral distribution of the LED light bulb is mainlybetween the wavelength ranges of about 400 nm to 800 nm. Moreover, thereare three peak wavelengths P1, P2, P3 in wavelength ranges correspondingto the light emitted by the LED light bulb. The wavelength of the peakvalue P1 is between about 430 nm and 480 nm, the wavelength of the peakvalue P2 is between about 580 nm and 620 nm, and the wavelength of thepeak value peak P3 is between about 680 nm and 750 nm. The lightintensity of the peak P1 is less than that of the peak P2, and the lightintensity of the peak P2 is less than the light intensity of the peakP3.

To make the above and other objects, features, and advantages of thepresent invention clearer and easier to understand, the followingembodiments will be described in detail with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more readily apparent to thoseordinarily skilled in the art after reviewing the following detaileddescription and accompanying drawings, in which:

FIGS. 1A to 1F are cross sectional views of various LED filaments inaccordance with the present invention;

FIG. 2 is a cross sectional view of an LED filament in accordance withan embodiment of the present invention;

FIG. 3 is a schematic view showing the interfaces passing through by thelight emitted by the LED chip in accordance with the present invention;

FIGS. 4A to 4I are schematic top views of a plurality of embodiments inaccordance with the present invention;

FIG. 5A is a schematic structural view showing an embodiment of alayered structure of an LED filament in accordance with the presentinvention;

FIG. 5B is a schematic structural view of an LED chip bonding wire of anembodiment in accordance with the present invention;

FIG. 6 shows the TMA analysis of the polyimide before and after addingthe thermal curing agent;

FIG. 7 shows the particle size distributions of the heat dispersingparticles with different specifications;

FIG. 8A shows the SEM image of an organosilicon-modified polyimide resincomposition composite film (substrate);

FIG. 8B shows the cross-sectional scheme of an organosilicon-modifiedpolyimide resin composition composite film (substrate) according to anembodiment of the present invention;

FIG. 8C shows the cross-sectional scheme of an organosilicon-modifiedpolyimide resin composition composite film (substrate) according toanother embodiment of the present disclosure;

FIG. 9A illustrates a perspective view of an LED light bulb according tothe third embodiment of the instant disclosure;

FIG. 9B illustrates an enlarged cross-sectional view of the dashed-linecircle of FIG. 9A;

FIG. 9C is a projection of a top view of an LED filament of the LEDlight bulb of FIG. 9A;

FIGS. 10A to 10D are respectively a perspective view, a side view,another side view and a top view of an LED light bulb in accordance withan embodiment of the present invention;

FIGS. 11A to 11D are respectively a perspective view, a side view,another side view and a top view of an LED light bulb in accordance withan embodiment of the present invention;

FIGS. 12A to 12D are respectively a perspective view, a side view,another side view and a top view of an LED light bulb in accordance withan embodiment of the present invention;

FIGS. 13A to 13D are respectively a perspective view, a side view,another side view and a top view of an LED light bulb in accordance withan embodiment of the present invention;

FIGS. 14A to 14D are respectively a perspective view, a side view,another side view and a top view of an LED light bulb in accordance withan embodiment of the present invention;

FIG. 15 is a schematic view showing the light emission spectrum of anLED light bulb in accordance with an embodiment of the presentinvention;

FIG. 16 is a schematic view showing the light emission spectrum of anLED light bulb in accordance with another embodiment of the presentinvention;

DETAILED DESCRIPTION

The present disclosure provides a novel LED filament and its applicationthe LED light bulb. The present disclosure will now be described in thefollowing embodiments with reference to the drawings. The followingdescriptions of various implementations are presented herein for purposeof illustration and giving examples only. This invention is not intendedto be exhaustive or to be limited to the precise form disclosed. Theseexample embodiments are just that—examples—and many implementations andvariations are possible that do not require the details provided herein.It should also be emphasized that the disclosure provides details ofalternative examples, but such listing of alternatives is notexhaustive. Furthermore, any consistency of detail between variousexamples should not be interpreted as requiring such detail—it isimpracticable to list every possible variation for every featuredescribed herein. The language of the claims should be referenced indetermining the requirements of the invention.

In the drawings, the size and relative sizes of components may beexaggerated for clarity. Like numbers refer to like elements throughout.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items and may beabbreviated as “/”.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers, or steps, these elements, components, regions, layers, and/orsteps should not be limited by these terms. Unless the context indicatesotherwise, these terms are only used to distinguish one element,component, region, layer, or step from another element, component,region, or step, for example as a naming convention. Thus, a firstelement, component, region, layer, or step discussed below in onesection of the specification could be termed a second element,component, region, layer, or step in another section of thespecification or in the claims without departing from the teachings ofthe present invention. In addition, in certain cases, even if a term isnot described using “first,” “second,” etc., in the specification, itmay still be referred to as “first” or “second” in a claim in order todistinguish different claimed elements from each other.

It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

It will be understood that when an element is referred to as being“connected” or “coupled” to or “on” another element, it can be directlyconnected or coupled to or on the other element or intervening elementsmay be present. In contrast, when an element is referred to as being“directly connected” or “directly coupled,” or “immediately connected”or “immediately coupled” to another element, there are no interveningelements present. Other words used to describe the relationship betweenelements should be interpreted in a like fashion (e.g., “between” versus“directly between,” “adjacent” versus “directly adjacent,” etc.).However, the term “contact,” as used herein refers to a directconnection (i.e., touching) unless the context indicates otherwise.

Embodiments described herein will be described referring to plan viewsand/or cross-sectional views by way of ideal schematic views.Accordingly, the exemplary views may be modified depending onmanufacturing technologies and/or tolerances. Therefore, the disclosedembodiments are not limited to those shown in the views, but includemodifications in configuration formed on the basis of manufacturingprocesses. Therefore, regions exemplified in figures may have schematicproperties, and shapes of regions shown in figures may exemplifyspecific shapes of regions of elements to which aspects of the inventionare not limited.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the figures. It will be understood thatthe spatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

Terms such as “same,” “equal,” “planar,” or “coplanar,” as used hereinwhen referring to orientation, layout, location, position, shapes,sizes, amounts, or other measures do not necessarily mean an exactlyidentical orientation, layout, location, position, shape, size, amount,or other measure, but are intended to encompass nearly identicalorientation, layout, location, position, shapes, sizes, amounts, orother measures within acceptable variations that may occur, for example,due to manufacturing processes. The term “substantially” may be usedherein to emphasize this meaning, unless the context or other statementsindicate otherwise. For example, items described as “substantially thesame,” “substantially equal,” or “substantially planar,” may be exactlythe same, equal, or planar, or may be the same, equal, or planar withinacceptable variations that may occur, for example, due to manufacturingprocesses.

Terms such as “about” or “approximately” may reflect sizes,orientations, or layouts that vary only in a small relative manner,and/or in a way that does not significantly alter the operation,functionality, or structure of certain elements. For example, a rangefrom “about 0.1 to about 1” may encompass a range such as a 0%-5%deviation around 0.1 and a 0% to 5% deviation around 1, especially ifsuch deviation maintains the same effect as the listed range.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the present invention belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent application, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

The LED chip units 102, 104, or named with the LED section 102, 104, maybe composed of a single LED chip, or two LED chips. Of course, it mayalso include multiple LED chips, that is, equal to or greater than threeLED chips.

FIGS. 1A to 1F are cross sectional views showing various embodiments ofthe LED filament in accordance with the present invention. As shown inFIG. 1A, the LED filament includes the LED chip units 102, 104, theconductive electrodes 110, 112, and the wires. The difference betweenthe present embodiment and the previous embodiment is the lightconversion layer 120 in the present embodiment is provided with a firstlight conversion layer 121 and a base layer 122. The upper surface ofthe base layer 122 is attached with a plurality of copper foils 116 andthe LED chip units 102 and 104. The copper foils 116 are located betweentwo adjacent LED chip units 102, 104. Wherein, the conductive electrodes110, 112 are disposed corresponding to the LED chip units 102, 104, andthe LED chip units 102, 104 and the copper foil 116, the LED chip units102, 104 and the conductive electrodes 110, 112 are electricallyconnected by wires respectively. The LED chip is provided with ap-junction and an n-junction, wherein the conductive wires comprise afirst wire 141 used for connecting the LED chip units 102, 104 with theconductive electrodes 110, 112, and a second wire 142 used forconnecting the LED chip units 102, 104 with the copper foil 116. Thefirst light conversion layer 121 covers a single LED chip unit and thefirst wire 141 and the second wire 142 connecting to the LED chip unit.The number of the first light conversion layers 121 is the same as thenumber of the LED chip unit. The LED light bulb employs the LED filamentas aforementioned designs, the heat dissipation function and the lightemitting efficiency of the LED filament are improved due to the thermalradiation area is increased. Furthermore, because the probability of thewire disconnection is reduced, the reliability of the LED light bulbproduct is increased, and also the brightness and illuminated appearanceof the LED filament with bending curve is achieved.

According to present embodiment, each of the LED chip units 102, 104includes two LED chips, and of course, may also include a plurality ofLED chips, that is, equal to or greater than three LED chips. Theexterior shape of the LED chip can be a strip type, but the presentinvention is not limited thereto. The strip type LED chip has fewerconductive electrodes, reducing the possibility of shielding the lightemitted by the LED chip. The LED chip units 102 and 104 are connected inseries and the conductive electrodes 110 and 112 are disposed at twoends of the connected LED chip units, and a portion of each of theconductive electrodes 110 and 112 is exposed outside the first lightconversion layer 121. Each of the six sides of every LED chip in the LEDchip units 102, 104 is covered by the first light conversion layer 121,that is, six sides of the LED chip of the LED units 102, 104 are coveredby a first light conversion layer 121, and covering coverage may bepartial overlap or as wrap but not limited to direct contact.Preferably, in the present embodiment, each of the six sides of the LEDchip of the LED chip units 102, 104 directly contacts the first lightconversion layer 121. However, in the implementation, the first lightconversion layer 121 may cover merely one of the six sides of each ofthe LED chip of the LED chip units 102, 104, that is, the first lightconversion layer 121 directly contacts the one side such as a top or abottom side. Similarly, the first light conversion layer 121 candirectly contact at least one side of the two conductive electrodes 110,112 or the copper foil 116.

The wire is a gold wire or an aluminum wire, and the combination of thecopper foil 116 and the gold wire to provide the LED filament having astabilized and a flexible conductive structure. The copper foil 116 canbe replaced by any other conductive material. The width or/and length ofthe opening of the copper foil 116 is larger than the contour of the LEDchip units 102, 104 and further to define the positions of the LED chipunits 102, 104. Furthermore, at least two of the six faces of the LEDchip units 102, 104 are contacted and covered by the first lightconversion layer 121. By utilizing the copper foil 116 and the wire aslinkage, a plurality of the LED chip units 102 and 104 areinterconnected in series, in parallel or in a combination of both. Then,the front end and the rear end of the interconnected LED chip units 102,104 are respectively connected to the two conductive electrodes 110, 112disposing on the base layer 122, and the conductive electrodes 110, 112are electrically connected to the power supply to provide theelectricity for emitting the LED chip units 102, 104.

The first light conversion layer 121 covers two ends of the copper foil116, wherein the covering area or the average thickness of the firstconversion layer 121 disposing on each of the two ends of the copperfoil 116 are substantially the same or not equal. The first lightconversion layer 121 covers the upper surface of the copper foil 116with an area ratio about 30 to 40 percent. In an embodiment of thepresent invention, as shown in the FIG. 1B, the first light conversionlayer 121 may cover the entire copper foil 116 disposing between the twoadjacent first light conversion layers. Wherein the covering area or theaverage thickness of the first conversion layer 121 disposing on the twoends of the copper foil 116 and on the middle of the copper foil 116 arenot equal. The first light conversion layer 121 covering the middlesurface of the copper foil has a thickness in a range of about 30 to 50micron (μm). The surface of the first light conversion layer 121 is anarc shape, and the height of the arc shape gradually decreases from themiddle to the both sides with respect to the base layer 122, and theangle between each of the two sides of the curved shape and the baselayer 122 is an acute angle or an obtuse angle.

The first light conversion layer 121 includes a phosphor gel or aphosphor film. At least a portion of each of the six sides of the LEDchip units 102, 104 directly contacts the first light conversion layer121 and/or one or both sides of each of the LED chip unit 102, 104 arebonded to the first light conversion layer 121 through the glue. In theaforementioned embodiment, the six sides the LED chip units 102, 104 areall covered by the first light conversion layer 121 and/or partiallydirect contacted with the first light conversion layer 121. Bothembodiments have equivalent concept. In some embodiments, the foregoingglue may also incorporate with phosphors to increase the overall lightconversion efficiency. The glue is usually also a silicon gel. Thedifference between the glue and the silicon gel is the glue generallymixed with silver powder or heat dissipating powder to improve thethermal conductivity.

As shown in FIG. 1C, the difference from the aforementioned embodimentis that the lower surface of the base layer 122 is covered by a secondlight conversion layer 123 with a uniform thickness. The upper surfaceand the lower surface of the base layer 122 are opposite to each other.As shown in FIG. 1D, the second light conversion layer 123 covering thelower surface of the base layer 122 has an inclined side or an inclinedside with an arc shape. The lower surface of the base layer 122 coveringby the second light conversion layer 123, the LED filament therefore cangenerate fluorescence with more yellow light and less blue light.Therefore, the difference in color temperature between the front andback surfaces of the LED chip units 102 and 104 can be reduced. Thereby,the color temperature of emitting light from both sides of the LED chipunits 102 and 104 is closer.

In one embodiment, as shown in FIG. 1E, the first light conversion layer121 covers two adjacent LED chip units 102, 104, a copper foil 116 islocated between two adjacent LED chip units 102, 104, and the first wire141 and the second wire 142 connecting between the LED chip units 102and 104. In one embodiment, a silver plating layer 118 is disposed onthe upper surface of the copper foil 116, and a portion of the copperfoil 116 located at the ends of the LED filament and extending beyondthe base layer 122 can serve as the conductive electrodes 110, 112. Thesilver plating layer 118 not only has good electrical conductivity butalso has the effect of increasing light reflection. The surface of thesilver plating layer 118 can be selectively provided with a solder masklayer (not shown), and the thickness of the solder mask layer is 30˜50um. The solder mask layer is obtained by an OSP (Organic SolderabilityPreservatives) process. The solder mask layer has functions of oxidationresistance, thermal shock resistance, and moisture resistance.

In another embodiment of the present invention, as shown in FIG. 1F, theLED filament 200 has LED chip units 102, 104, conductive electrodes 110,112, wires 140, and a light conversion layer 120. The copper foil 116 islocated between the adjacent two LED chip units 102, 104, the conductiveelectrodes 110, 112 are arranged corresponding to the LED chip units102, 104, and the LED chip units 102, 104 and the copper foil 116, theLED chip units 102, 104 and the conductive electrodes 110, 112 areelectrically connected by wire 140 respectively. The light conversionlayer 120 is disposed on the LED chip units 102, 104 and at least twosides of conductive electrodes 110, 112. The light conversion layer 120exposes a portion of each of the conductive electrodes 110, 112 of theLED filament, and the light conversion layer 120 includes a phosphorlayer 124 and a silicon layer 125. The phosphor layer 124 directlycontacts the surfaces of the LED chip unit 102, 104. In the phosphorsspraying process, the phosphors may be sprayed on the surfaces of theLED chip unit 102, 104, the copper foil 116, the conductive electrodes110, 112 and the wire 140 by electrostatic spraying to form the phosphorlayer 124. Then, the vacuum coating method can be used to disposing asilicon layer 125 on the phosphor layer 124, wherein the silicon layer125 does not contain phosphor. The thickness of the phosphor layer 124and the silicon layer 125 are equal or unequal. The thickness of thephosphor layer 124 and silicon layer 125 respectively is about 30 to 70micron (um) and 30 to 50 micron (um). In another embodiment, thesurfaces of the LED chip units 102, 104, the copper foil 116, theconductive electrodes 110, 112, and the wires 140 may be covered with atransparent resin layer, and the transparent resin layer does notcontain phosphors, and then covered by phosphors powder on thetransparent resin layer. The thickness of the transparent resin layerand the phosphor layer are equal or unequal, and the thickness of thetransparent resin layer is about 30 to 50 micron (um).

Referring to FIG. 2, in the LED filament structure shown in FIG. 2, theLED filament 400 has a light conversion layer 420, the LED sections 402,404, the conductive electrodes 410, 412, and at least one conductivesection 430. The conductive section 430 is located between adjacent LEDsections 402 and 404. The LED sections 402 and 404 include at least twoLED chips 442 electrically connected to each other through the wires440. In the present embodiment, the conductive section 430 includes aconductor 430 a. The conductive section 430 and the LED sections 402,404 are electrically connected by wires 450, that is, two LED chipsrespectively located in the adjacent two LED sections 402, 404 andclosest to the conductive section 430 are electrically connected to eachother through the wires 450 connecting with the conductor 430 a in theconductive section 430. The length of the conductive section 430 isgreater than the distance between two adjacent LED chips in one singleLED sections 402, 404, and the length of the wire 440 is less than thelength of the conductor 430 a. The light conversion layer 420 isdisposed on at least one side of the LED chip 442 and the conductiveelectrode 410, 412, and a part of the two conductive electrodes isexposed from the light conversion layer. The light conversion layer 420includes at least a top layer 420 a and a base layer 420 b. In thepresent embodiment, the LED sections 402, 404, the conductive electrodes410, 412, and the conductive section 430 are all attached to the baselayer 420 b.

The conductor 430 a can be a copper foil or other electricallyconductive material, and the conductor 430 a has opening. The uppersurface of the conductor 430 a may further have a silver plating layer,and subsequently, the LED chip 442 may be attached to the base layer 420b by means of die bond paste or the like. Thereafter, a phosphor glue orphosphor film is applied to coat over the LED chip 442, the wires 440,450, and a portion of the conductive electrodes 410, 412 to form a lightconversion layer 420. The width or/and the length of the opening of theconductor 430 a are respectively larger than the width or/and the lengthof the LED chip 442 and defining the position of the LED chip 442. Atleast two of the six faces of the LED chip, generally five faces in thepresent embodiment, being covered by the phosphor glue. The wires 440,450 may be gold wires. In the present embodiment, the combination ofcopper foil 460 and the gold wire 440 provides a solid conductivestructure and also maintaining the flexibleness of the LED filament.Besides, the silver plating layer 461 has an effect of increasing lightreflection in addition to good electrical conductivity.

When the LED filament is illuminated in an LED light bulb encapsulationwith the inert gas, as shown in FIG. 3, the light emitted by the LEDchip 442 passes through the interfaces A, B, C, D, E and F respectively,wherein the interface A is the interface between the p-GaN gate and thetop layer 420 a in the LED chip 442. The interface B is the interfacebetween the top layer 420 a and the inert gas, the interface C is theinterface between the substrate and the paste 450 (e.g., die bond paste)in the LED chip 442, the D interface is the interface between the paste450 and the base layer 420 b, the interface E is the interface betweenthe base layer 420 b and the inert gas, and the interface F is theinterface between the base layer 420 b and the top layer 420 a. Whenlight passes through the interfaces A, B, C, D, E and F respectively,the refractive index of the two substances in any interface is n1 and n2respectively, then |n1−n2|<1.0, preferably |n1−n2|<0.5, more preferably|n1−n2|<0.2. In one embodiment, the refractive index of two substancesin any one of the four interfaces of B, E, D and F is n1 and n2respectively, and then |n1−n2|<1.0, preferably |n1−n2|<0.5, Morepreferably |n1−n2|<0.2. In one embodiment, the refractive index of twosubstances in any interface of D and F two interfaces is n1 and n2respectively, then |n1−n2|<1.0, preferably |n1−n2|<0.5, preferably|n1−n2|<0.2. The absolute value of the difference in refractive index ofthe two substances in each interface is smaller, the light emittingefficiency is higher. For example, when the light emitted by the LEDchip 442 passes from the base layer 420 b to the top layer 420 a, theincident angle is θ1, the refraction angle is θ2, and the refractiveindex of the base layer 420 b is n1, and the refractive index of the toplayer 420 a is n2, according to the equation sin θ1/sin θ2=n2/n1, whenthe absolute value of the difference between n1 and n2 is smaller, theincident angle closer to the refraction angle, and then thelight-emitting efficiency of the LED filament is higher.

Next, a chip bonding design relating to an LED filament will bedescribed. The FIG. 4A is a top view of an embodiment of the LEDfilament 300 in an unbent state in accordance with the presentinvention. The LED filament 300 includes a plurality of LED chip units302, 304, a conductor 330 a, and at least two conductive electrodes 310,312. The LED chip units 302 and 304 may be a single LED chip, or mayinclude a plurality of LED chips, that is, equal to or greater than twoLED chips.

The conductor 330 a is located between the adjacent two LED chip units302, 304, the LED chip units 302, 304 are at different positions in theY direction, and the conductive electrodes 310, 312 are disposedcorresponding to the LED chip units 302, 304 and electrically connectedto the LED chip units 302 and 304 through the wires 340. The adjacenttwo LED chip units 302 and 304 are electrically connected to each otherthrough the conductor 330 a. The angle between the conductor 330 a andthe LED filament in the longitudinal direction (X direction) is 30° to120°, preferably 60° to 120°. In the related art, the direction of theconductor 330 a is parallel to the X direction, and the internal stressacting on the cross sectional area of the conductor is large when thefilament is bent at the conductor. Therefore, the conductor 330 a isdisposed at a certain angle with the X direction and it can effectivelyreduce the internal stress thereof. The wire 340 is at an angle,parallel, vertical or any combination with the X direction. In theembodiment, the LED filament 300 includes two wires 340, one wire 340 isparallel to the X direction, and the other wire 340 has an angle of 30°to 120° with respect to the X direction. The LED filament 300 emitslight after its conductive electrodes 310, 312 are powered with voltagesource or current source.

FIGS. 4B to 4D show the case where the conductor 330 a is 90° withrespect to the X direction, that is, the conductor 330 a isperpendicular to the X direction, which can reduce the internal stresson the conductor cross sectional area when the filament is bent. In someembodiment the wire 340 both in parallel and vertically with respect tothe X direction are combined in an LED filament, as shown in FIG. 4B,the LED filament 300 includes two wires 340, one wire 340 being parallelto the X direction and the other wire 340 being perpendicular to the Xdirection.

As shown in FIG. 4C, the difference from the embodiment shown in FIG. 4Bis that the wire 340 is perpendicular to the X direction, and thebendability duration between the conductive electrodes 310, 312 and theLED chip units 302, 304 is improved. Further, since the conductor 330 aand the wire 340 are simultaneously arranged to be perpendicular to theX direction, the LED filament can have good bendability at any position.

FIG. 4E is a top view of the LED filament 300 in an unbent state inaccordance with one embodiment of the present invention. FIG. 4E differsfrom the embodiment shown in FIG. 4C is that, in the X direction, theLED chip unit 304 is between two adjacent LED chip units 302, and nooverlap with the LED chip unit 302 in the projection in the Y direction,so that when the LED filament is bent at the conductor 330 a, the LEDchip is not damaged, thereby improving the stability of the LED lightbulb product quality.

As shown in FIG. 4F, the LED filament 300 includes a plurality of LEDchip units 302, 304, a conductor 330 a, and at least two conductiveelectrodes 310, 312. The conductor 330 a is located between adjacent LEDchip units 302, 304, and the LED chip units 302, 304 are disposed atsubstantially the same position in the Y direction, so that the overallwidth of the LED filament 300 is smaller, thereby shortening the thermaldissipation path of the LED chip and improving the thermal dissipationeffect. The conductive electrodes 310, 312 are correspondingly arrangedto the LED chip units 302, 304, and are electrically connected to theLED chip units 302, 304 through the wires 340. The LED chip units302/304 are electrically connected to the conductors 330 a through thewires 350, and the conductors 330 a are in the font shape like deformedZ letter. The aforesaid shape can increase the mechanical strength ofthe region where the conductor and the LED chip are located in, and canavoid the damage of the wire connecting the LED chip and the conductorwhen the LED filament 300 is bent. At the same time, the wire 340 isdisposed in a parallel with the X direction.

As shown in FIG. 4G, the LED filament 300 includes a plurality of LEDchip units 302, 304, at least one conductor 330 a, and at least twoconductive electrodes 310, 312. The LED chip units 302, 304 are in thesame position in the Y direction, and the conductor 330 a parallel tothe X direction, the conductor 330 a includes a first conductor 3301 aand a second conductor 3302 a, respectively located on opposite sides ofthe LED chip unit 302/304, and the first conductor 3301 a is locatedbetween adjacent LED chip units 302, 304 and electrically connected tothe LED chip unit 302/304 through the wire 350. The wire 350 isperpendicular to the X direction, and reduces the internal stress on thecross sectional area of the wire when the LED filament 300 is bent,thereby improving the bendability of the wire. The second conductor 3302a is not electrically connected to the LED chip units 302, 304, and thesecond conductor 3302 a extends along the X direction to the one end ofeach wire 340 adjacent to the electrode. When the LED filament 300 issuffered external force, it can play the role of stress buffering,protect the LED chip, improve product stability, and secondly make theforce balance on both sides of the LED chip. The conductive electrodes310, 312 are configured corresponding to the LED chip units 302, 304,and are electrically connected to the LED chip units 302, 304 throughwires 340.

As shown in FIG. 4H, the difference from the embodiment shown in FIG. 4Gis that the first conductor 3301 a and the second conductor 3302 aextends along the X direction to the one end of each wire 340 adjacentto the electrode, and the first conductor 3301 a and the secondconductor 3302 a are electrically connected to both the LED chip unit302 and the LED chip unit 304 by wires 350. In other embodiments, forexample, the first conductor 3301 a is electrically connected to the LEDchip unit 302 and the LED chip unit 304 through the wire 350, and thesecond conductor 3302 a may not be electrically connected to the LEDchip unit 302/304. By setting conductors on both sides of the LED chip,when the LED filament 300 is bent, it can not only increase the strengthof the LED filament 300 but also disperse the heat generated by the LEDchips during illumination.

FIG. 4I is a top view showing an embodiment of the LED filament 300 inan unbent state. In the present embodiment, the LED chip units 302 and304 are single LED chips, and the width of the LED chip units 302 and304 is parallel to the X direction. Preferably, the LED chip units 302and 304 are at substantially the same position in the Y direction, sothat the overall width of the LED filament 300 is smaller, therebyshortening the heat dissipation path of the LED chip and improving thethermal dissipation effect. The adjacent two LED chip units 302 and 304are connected by a conductor 330 a, and the angle between the conductor330 a and the X direction is 30° to 120°, which reduces the internalstress on the cross sectional area of the wire and also improves thebendability of the wire when the LED filament 300 is bent. In otherembodiments, the LED chip unit longitudinally may have an angle with theX direction as the conductor 330 a, which may further reduce the overallwidth of the LED filament 300.

FIG. 5A is a schematic view showing an embodiment of a layered structureof the LED filament 400 of the present invention. The LED filament 400has a light conversion layer 420, two LED chip units 402, 404, twoconductive electrodes 410, 412, and a conductive section 430 forelectrically connecting adjacent two LED chip units 402, 404. Each ofthe LED chip units 402, 404 includes at least two LED chips 442 that areelectrically connected to each other by wires 440. In the presentembodiment, the conductive section 430 includes a conductor 430, and theconductive section 430 is electrically connected to the LED sections402, 404 through the wires 450. The shortest distance between the twoLED chips 442 located in the adjacent two LED chip units 402, 404 isgreater than the distance between adjacent two LED chips in the samechip unit 402/404. Moreover, the length of wire 440 is less than thelength of conductor 430 a. The light conversion layer 420 is disposed onthe LED chip 442 and at least two sides of the conductive electrodes410, 412. The light conversion layer 420 exposes a portion of theconductive electrodes 410, 412. The light conversion layer 420 maycomposed of at least one top layer 420 a and one base layer 420 b as theupper layer and the lower layer of the LED filament respectively. In thepresent embodiment, the LED chips 442 and the conductive electrodes 410,412 are sandwiched in between the top layer 420 a and the base layer 420b. When the wire bonding process of the face up chip is carried outalong the x direction, for example, the bonding wire and the bondingconductor are gold wires, the quality of the bonding wire is mainlydetermined by the stress at the five points A, B, C, D, and E as shownin FIG. 5B. The point A is the junction of the soldering pad 4401 andthe gold ball 4403, point B is the junction of the gold ball 4403 andthe gold wire 440, point C is between the two segments of the gold wire440, point D is the gold wire 440 and the two solder butted joints 4402,and the point E is between the two solder butted joints 4402 and thesurface of the chip 442. Because of point B is the first bending pointof the gold wire 440, and the gold wire 440 at the point D is thinner,thus gold wire 440 is frangible at points B and D. So that, for example,in the implementation of the structure of the LED filament 300 packageshowing in FIG. 5A, the top layer 420 a only needs to cover points B andD, and a portion of the gold wire 440 is exposed outside the lightconversion layer. If the one of the six faces of the LED chip 442farthest from the base layer 420 b is defined as the upper surface ofthe LED chip 442, the distance from the upper surface of the LED chip442 to the surface of the top layer 420 a is in a range of around 100 to200 μm.

The next part will describe the material of the filament of the presentinvention. The material suitable for manufacturing a filament substrateor a light-conversion layer for LED should have properties such asexcellent light transmission, good heat resistance, excellent thermalconductivity, appropriate refraction rate, excellent mechanicalproperties and good warpage resistance. All the above properties can beachieved by adjusting the type and the content of the main material, themodifier and the additive contained in the organosilicon-modifiedpolyimide composition. The present disclosure provides a filamentsubstrate or a light-conversion layer formed from a compositioncomprising an organosilicon-modified polyimide. The composition can meetthe requirements on the above properties. In addition, the type and thecontent of one or more of the main material, the modifier (thermalcuring agent) and the additive in the composition can be modified toadjust the properties of the filament substrate or the light-conversionlayer, so as to meet special environmental requirements. Themodification of each property is described herein below.

Adjustment of the Organosilicon-Modified Polyimide

The organosilicon-modified polyimide provided herein comprises arepeating unit represented by the following general Formula (I):

In general Formula (I), Ar¹ is a tetra-valent organic group. The organicgroup has a benzene ring or an alicyclic hydrocarbon structure. Thealicyclic hydrocarbon structure may be monocyclic alicyclic hydrocarbonstructure or a bridged-ring alicyclic hydrocarbon structure, which maybe a dicyclic alicyclic hydrocarbon structure or a tricyclic alicyclichydrocarbon structure. The organic group may also be a benzene ring oran alicyclic hydrocarbon structure comprising a functional group havingactive hydrogen, wherein the functional group having active hydrogen isone or more of hydroxyl, amino, carboxy, amido and mercapto.

Ar² is a di-valent organic group, which organic group may have forexample a monocyclic alicyclic hydrocarbon structure or a di-valentorganic group comprising a functional group having active hydrogen,wherein the functional group having active hydrogen is one or more ofhydroxyl, amino, carboxy, amido and mercapto.

R is each independently methyl or phenyl.

n is 1˜5, preferably 1, 2, 3 or 5.

The polymer of general Formula (I) has a number average molecular weightof 5000˜100000, preferably 10000˜60000, more preferably 20000˜40000. Thenumber average molecular weight is determined by gel permeationchromatography (GPC) and calculated based on a calibration curveobtained by using standard polystyrene. When the number averagemolecular weight is below 5000, a good mechanical property is hard to beobtained after curing, especially the elongation tends to decrease. Onthe other hand, when it exceeds 100000, the viscosity becomes too highand the resin is hard to be formed.

Ar¹ is a component derived from a dianhydride, which may be an aromaticanhydride or an aliphatic anhydride. The aromatic anhydride includes anaromatic anhydride comprising only a benzene ring, a fluorinatedaromatic anhydride, an aromatic anhydride comprising amido group, anaromatic anhydride comprising ester group, an aromatic anhydridecomprising ether group, an aromatic anhydride comprising sulfide group,an aromatic anhydride comprising sulfonyl group, and an aromaticanhydride comprising carbonyl group.

Examples of the aromatic anhydride comprising only a benzene ringinclude pyromellitic dianhydride (PMDA), 2,3,3′,4′-biphenyltetracarboxylic dianhydride (aBPDA), 3,3′,4,4′-biphenyl tetracarboxylicdianhydride (sBPDA), and4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA). Examples of thefluorinated aromatic anhydride include4,4′-(hexafluoroisopropylidene)diphthalic anhydride which is referred toas 6FDA. Examples of the aromatic anhydride comprising amido groupincludeN,N′-(5,5′-(perfluoropropane-2,2-diyl)bis(2-hydroxy-5,1-phenylene))bis(1,3-dioxo-1,3-dihydroisobenzofuran)-5-arboxamide)(6FAP-ATA), andN,N′-(9H-fluoren-9-ylidenedi-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxamide] (FDA-ATA). Examples of the aromatic anhydride comprisingester group include p-phenylene bis(trimellitate) dianhydride (TAHQ).Examples of the aromatic anhydride comprising ether group include4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA),4,4′-oxydiphthalic dianhydride (sODPA), 2,3,3′,4′-diphenyl ethertetracarboxylic dianhydride (aODPA), and4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride)(BPADA).Examples of the aromatic anhydride comprising sulfide group include4,4′-bis(phthalic anhydride)sulfide (TPDA). Examples of the aromaticanhydride comprising sulfonyl group include3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA). Examples ofthe aromatic anhydride comprising carbonyl group include3,3′,4,4′-benzophenonetetracarboxylic dianhydride(BTDA).

The alicyclic anhydride includes 1,2,4,5-cyclohexanetetracarboxylic aciddianhydride which is referred to as HPMDA, 1,2,3,4-butanetetracarboxylicdianhydride (BDA),tetrahydro-1H-5,9-methanopyrano[3,4-d]oxepine-1,3,6,8(4H)-tetrone (TCA),hexahydro-4,8-ethano-1H,3H-benzo [1,2-C′]difuran-1,3,5,7-tetrone (BODA),cyclobutane-1,2,3,4-tetracarboxylic dianhydride(CBDA), and1,2,3,4-cyclopentanetetracarboxylic dianhydride (CpDA); or alicyclicanhydride comprising an olefin structure, such asbicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (COeDA).When an anhydride comprising ethynyl such as4,4′-(ethyne-1,2-diyl)diphthalic anhydride (EBPA) is used, themechanical strength of the light-conversion layer can be further ensuredby post-curing.

Considering the solubility, 4,4′-oxydiphthalic anhydride (sODPA),3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA),cyclobutanetetracarboxylic dianhydride (CBDA) and4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) arepreferred. The above dianhydride can be used alone or in combination.

Ar² is derived from diamine which may be an aromatic diamine or analiphatic diamine. The aromatic diamine includes an aromatic diaminecomprising only a benzene ring, a fluorinated aromatic diamine, anaromatic diamine comprising ester group, an aromatic diamine comprisingether group, an aromatic diamine comprising amido group, an aromaticdiamine comprising carbonyl group, an aromatic diamine comprisinghydroxyl group, an aromatic diamine comprising carboxy group, anaromatic diamine comprising sulfonyl group, and an aromatic diaminecomprising sulfide group.

The aromatic diamine comprising only a benzene ring includesm-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene,2,6-diamino-3,5-diethyltoluene, 3,3′-dimethylbiphenyl-4,4′-diamine9,9-bis(4-aminophenyl)fluorene (FDA),9,9-bis(4-amino-3-methylphenyl)fluorene, 2,2-bis(4-aminophenyl)propane,2,2-bis(3-methyl-4-aminophenyl)propane,4,4′-diamino-2,2′-dimethylbiphenyl(APB). The fluorinated aromaticdiamine includes 2,2′-bis(trifluoromethyl)benzidine (TFMB),2,2-bis(4-aminophenyl)hexafluoropropane (6FDAM),2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP), and2,2-bis(3-amino-4-methylphenyl)hexafluoropropane (BIS-AF-AF). Thearomatic diamine comprising ester group includes[4-(4-aminobenzoyl)oxyphenyl]4-aminobenzoate (ABHQ),bis(4-aminophenyl)terephthalate(BPTP), and 4-aminophenyl 4-aminobenzoate(APAB). The aromatic diamine comprising ether group includes2,2-bis[4-(4-aminophenoxy)phenyl]propane)(BAPP),2,2′-bis[4-(4-aminophenoxy)phenyl]propane (ET-BDM),2,7-bis(4-aminophenoxy)-naphthalene (ET-2,7-Na),1,3-bis(3-aminophenoxy)benzene (TPE-M),4,4′-[1,4-phenyldi(oxy)]bis[3-(trifluoromethyl)aniline] (p-6FAPB),3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether (ODA),1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(4-aminophenoxy)benzene(TPE-Q), and 4,4′-bis(4-aminophenoxy)biphenyl(BAPB). The aromaticdiamine comprising amido group includesN,N′-bis(4-aminophenyl)benzene-1,4-dicarboxamide (BPTPA), 3,4′-diaminobenzanilide (m-APABA), and 4,4′-diaminobenzanilide (DABA). The aromaticdiamine comprising carbonyl group includes 4,4′-diaminobenzophenone(4,4′-DABP), and bis(4-amino-3-carboxyphenyl) methane (or referred to as6,6′-diamino-3,3′-methylanediyl-dibenzoic acid). The aromatic diaminecomprising hydroxyl group includes 3,3′-dihydroxybenzidine (HAB), and2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP). The aromaticdiamine comprising carboxy group includes6,6′-diamino-3,3′-methylanediyl-dibenzoic acid (MBAA), and3,5-diaminobenzoic acid (DBA). The aromatic diamine comprising sulfonylgroup includes 3,3′-diaminodiphenyl sulfone (DDS),4,4′-diaminodiphenylsulfone, bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS) (or referred to as4,4′-bis(4-aminophenoxy)diphenylsulfone), and3,3′-diamino-4,4′-dihydroxydiphenyl sulfone (ABPS). The aromatic diaminecomprising sulfide group includes 4,4′-diaminodiphenyl sulfide.

The aliphatic diamine is a diamine which does not comprise any aromaticstructure (e.g., benzene ring). The aliphatic diamine includesmonocyclic alicyclic amine and straight chain aliphatic diamine, whereinthe straight chain aliphatic diamine include siloxane diamine, straightchain alkyl diamine and straight chain aliphatic diamine comprisingether group. The monocyclic alicyclic diamine includes4,4′-diaminodicyclohexylmethane (PACM), and3,3′-dimethyl-4,4-diaminodicyclohexylmethane (DMDC). The siloxanediamine (or referred to as amino-modified silicone) includesα,ω-(3-aminopropyl)polysiloxane (KF8010), X22-161A, X22-161B, NH15D, and1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (PAME). Thestraight chain alkyl diamine has 6˜12 carbon atoms, and is preferablyun-substituted straight chain alkyl diamine. The straight chainaliphatic diamine comprising ether group includes ethylene glycoldi(3-aminopropyl) ether.

The diamine can also be a diamine comprising fluorenyl group. Thefluorenyl group has a bulky free volume and rigid fused-ring structure,which renders the polyimide good heat resistance, thermal and oxidationstabilities, mechanical properties, optical transparency and goodsolubility in organic solvents. The diamine comprising fluorenyl group,such as 9,9-bis(3,5-difluoro-4-aminophenyl)fluorene, may be obtainedthrough a reaction between 9-fluorenone and 2,6-dichloroaniline. Thefluorinated diamine can be1,4-bis(3′-amino-5′-trifluoromethylphenoxy)biphenyl, which is ameta-substituted fluorine-containing diamine having a rigid biphenylstructure. The meta-substituted structure can hinder the charge flowalong the molecular chain and reduce the intermolecular conjugation,thereby reducing the absorption of visible lights. Using asymmetricdiamine or anhydride can increase to some extent the transparency of theorganosilicon-modified polyimide resin composition. The above diaminescan be used alone or in combination.

Examples of diamines having active hydrogen include diamines comprisinghydroxyl group, such as 3,3′-diamino-4,4′-dihydroxybiphenyl,4,4′-diamino-3,3′-dihydroxy-1,1′-biphenyl (or referred to as3,3′-dihydroxybenzidine) (HAB),2,2-bis(3-amino-4-hydroxyphenyl)propane(BAP),2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane(6FAP),1,3-bis(3-hydro-4-aminophenoxy) benzene,1,4-bis(3-hydroxy-4-aminophenyl)benzene and3,3′-diamino-4,4′-dihydroxydiphenyl sulfone (ABPS). Examples of diaminescomprising carboxy group include 3,5-diaminobenzoic acid,bis(4-amino-3-carboxyphenyl)methane (or referred to as6,6′-diamino-3,3′-methylenedibenzoic acid),3,5-bis(4-aminophenoxy)benzoic acid, and1,3-bis(4-amino-2-carboxyphenoxy)benzene. Examples of diaminescomprising amino group include 4,4′-diaminobenzanilide (DABA),2-(4-aminophenyl)-5-aminobenzoimidazole, diethylenetriamine,3,3′-diaminodipropylamine, triethylenetetramine, andN,N′-bis(3-aminopropyl)ethylenediamine (or referred to asN,N-di(3-aminopropyl)ethylethylamine). Examples of diamines comprisingthiol group include 3,4-diaminobenzenethiol. The above diamines can beused alone or in combination.

The organosilicon-modified polyimide can be synthesized by well-knownsynthesis methods. For example, it can be prepared from a dianhydrideand a diamine which are dissolved in an organic solvent and subjected toimidation in the presence of a catalyst. Examples of the catalystinclude acetic anhydride/triethylamine, and valerolactone/pyridine.Preferably, removal of water produced in the azeotropic process in theimidation is promoted by using a dehydrant such as toluene.

Polyimide can also be obtained by carrying out an equilibrium reactionto give a poly (amic acid) which is heated to dehydrate. In otherembodiments, the polyimide backbone may have a small amount of amicacid. For example, the ratio of amic acid to imide in the polyimidemolecule may be 1˜3:100. Due to the interaction between amic acid andthe epoxy resin, the substrate has superior properties. In otherembodiments, a solid state material such as a thermal curing agent,inorganic heat dispersing particles and phosphor can also be added atthe state of poly (amic acid) to give the substrate. In addition,solubilized polyimide can also be obtained by direct heating anddehydration after mixing of alicylic anhydride and diamine. Suchsolubilized polyimide, as an adhesive material, has a good lighttransmittance. In addition, it is liquid state per se; therefore, othersolid materials (such as the inorganic heat dispersing particles and thephosphor) can be dispersed in the adhesive material more sufficiently.

In one embodiment for preparing the organosilicon-modified polyimide,the organosilicon-modified polyimide can be produced by dissolving thepolyimide obtained by heating and dehydration after mixing a diamine andan anhydride and a siloxane diamine in a solvent. In another embodiment,the amidic acid, before converting to polyimide, is reacted with thesiloxane diamine.

In addition, the polyimide compound may be obtained by dehydration andring-closing and condensation polymerization from an anhydride and adiamine, such as an anhydride and a diamine in a molar ratio of 1:1. Inone embodiment, 200 micromole (mmol) of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride(6FDA), 20 micromole (mmol) of2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane(6FAP), 50 micromole(mmol) of 2,2′-di(trifluoromethyl)diaminobiphenyl(TFMB) and 130micromole (mmol) of aminopropyl-terminated poly(dimethylsiloxane) areused to give the PI synthesis solution.

The above methods can be used to produce amino-terminated polyimidecompounds. However, other methods can be used to producecarboxy-terminated polyimide compounds. In addition, in the abovereaction between anhydride and diamine, where the backbone of theanhydride comprises a carbon-carbon triple bond, the affinity of thecarbon-carbon triple bond can promote the molecular structure.Alternatively, a diamine comprising vinyl siloxane structure can beused.

The molar ratio of dianhydride to diamine may be 1:1. The molarpercentage of the diamine comprising a functional group having activehydrogen may be 5˜25% of the total amount of diamine. The temperatureunder which the polyimide is synthesized is preferably 80˜250° C., morepreferably 100˜200° C. The reaction time may vary depending on the sizeof the batch. For example, the reaction time for obtaining 10˜30 gpolyimide is 6˜10 hours.

The organosilicon-modified polyimide can be classified as fluorinatedaromatic organosilicon-modified polyimides and aliphaticorganosilicon-modified polyimides. The fluorinated aromaticorganosilicon-modified polyimides are synthesized from siloxane-typediamine, aromatic diamine comprising fluoro (F) group (or referred to asfluorinated aromatic diamine) and aromatic dianhydride comprising fluoro(F) group (or referred to as fluorinated aromatic anhydride). Thealiphatic organosilicon-modified polyimides are synthesized fromdianhydride, siloxane-type diamine and at least one diamine notcomprising aromatic structure (e.g., benzene ring) (or referred to asaliphatic diamine), or from diamine (one of which is siloxane-typediamine) and at least one dianhydride not comprising aromatic structure(e.g., benzene ring) (or referred to as aliphatic anhydride). Thealiphatic organosilicon-modified polyimide includes semi-aliphaticorganosilicon-modified polyimide and fully aliphaticorganosilicon-modified polyimide. The fully aliphaticorganosilicon-modified polyimide is synthesized from at least onealiphatic dianhydride, siloxane-type diamine and at least one aliphaticdiamine. The raw materials for synthesizing the semi-aliphaticorganosilicon-modified polyimide include at least one aliphaticdianhydride or aliphatic diamine. The raw materials required forsynthesizing the organosilicon-modified polyimide and the siloxanecontent in the organosilicon-modified polyimide would have certaineffects on transparency, chromism, mechanical property, warpage extentand refractivity of the substrate.

The organosilicon-modified polyimide of the present disclosure has asiloxane content of 20˜75 wt %, preferably 30˜70 wt %, and a glasstransition temperature of below 150° C. The glass transition temperature(Tg) is determined on TMA-60 manufactured by Shimadzu Corporation afteradding a thermal curing agent to the organosilicon-modified polyimide.The determination conditions include: load: 5 gram; heating rate: 10°C./min; determination environment: nitrogen atmosphere; nitrogen flowrate: 20 ml/min; temperature range: −40 to 300° C. When the siloxanecontent is below 20%, the film prepared from the organosilicon-modifiedpolyimide resin composition may become very hard and brittle due to thefilling of the phosphor and thermal conductive fillers, and tend to warpafter drying and curing, and therefore has a low processability. Inaddition, its resistance to thermochromism becomes lower. On the otherhand, when the siloxane content is above 75%, the film prepared from theorganosilicon-modified polyimide resin composition becomes opaque, andhas reduced transparency and tensile strength. Here, the siloxanecontent is the weight ratio of siloxane-type diamine (having a structureshown in Formula (A)) to the organosilicon-modified polyimide, whereinthe weight of the organosilicon-modified polyimide is the total weightof the diamine and the dianhydride used for synthesizing theorganosilicon-modified polyimide subtracted by the weight of waterproduced during the synthesis.

Wherein R is methyl or phenyl, preferably methyl, n is 1˜5, preferably1, 2, 3 or 5.

The only requirements on the organic solvent used for synthesizing theorganosilicon-modified polyimide are to dissolve theorganosilicon-modified polyimide and to ensure the affinity(wettability) to the phosphor or the fillers to be added. However,excessive residue of the solvent in the product should be avoided.Normally, the number of moles of the solvent is equal to that of waterproduced by the reaction between diamine and anhydride. For example, 1mol diamine reacts with 1 mol anhydride to give 1 mol water; then theamount of solvent is 1 mol. In addition, the organic solvent used has aboiling point of above 80° C. and below 300° C., more preferably above120° C. and below 250° C., under standard atmospheric pressure. Sincedrying and curing under a lower temperature are needed after coating, ifthe temperature is lower than 120° C., good coating cannot be achieveddue to high drying speed during the coating process. If the boilingpoint of the organic solvent is higher than 250° C., the drying under alower temperature may be deferred. Specifically, the organic solvent maybe an ether-type organic solvent, an ester-type organic solvent, adimethyl ether-type organic solvent, a ketone-type organic solvent, analcohol-type organic solvent, an aromatic hydrocarbon solvent or othersolvents. The ether-type organic solvent includes ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, propylene glycolmonomethyl ether, propylene glycol monoethyl ether, ethylene glycoldimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutylether, diethylene glycol dimethyl ether, diethylene glycol diethylether, diethylene glycol methyl ethyl ether, dipropylene glycol dimethylether or diethylene glycol dibutyl ether, and diethylene glycol butylmethyl ether. The ester-type organic solvent includes acetates,including ethylene glycol monoethyl ether acetate, diethylene glycolmonobutyl ether acetate, propylene glycol monomethyl ether acetate,propyl acetate, propylene glycol diacetate, butyl acetate, isobutylacetate, 3-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, benzylacetate and 2-(2-butoxyethoxy)ethyl acetate; and methyl lactate, ethyllactate, n-butyl acetate, methyl benzoate and ethyl benzoate. Thedimethyl ether-type solvent includes triethylene glycol dimethyl etherand tetraethylene glycol dimethyl ether. The ketone-type solventincludes acetylacetone, methyl propyl ketone, methyl butyl ketone,methyl isobutyl ketone, cyclopentanone, and 2-heptanone. Thealcohol-type solvent includes butanol, isobutanol, isopentanol,4-methyl-2-pentanol, 3-methyl-2-butanol, 3-methyl-3-methoxybutanol, anddiacetone alcohol. The aromatic hydrocarbon solvent includes toluene andxylene. Other solvents include y-butyrolactone, N-methylpyrrolidone, N,N-dimethylformamide, N, N-dimethylacetamide and dimethyl sulfoxide.

The present disclosure provides an organosilicon-modified polyimideresin composition comprising the above organosilicon-modified polyimideand a thermal curing agent, which may be epoxy resin, hydrogenisocyanate or bisoxazoline compound. In one embodiment, based on theweight of the organosilicon-modified polyimide, the amount of thethermal curing agent is 5˜12% of the weight of theorganosilicon-modified polyimide. The organosilicon-modified polyimideresin composition may further comprise heat dispersing particles andphosphor.

Light Transmittance

The factors affecting the light transmittance of theorganosilicon-modified polyimide resin composition at least include thetype of the main material, the type of the modifier(thermal curingagent), the type and content of the heat dispersing particles, and thesiloxane content. Light transmittance refers to the transmittance of thelight near the main light-emitting wavelength range of the LED chip. Forexample, blue LED chip has a main light-emitting wavelength of around450 nm, then the composition or the polyimide should have low enough oreven no absorption to the light having a wavelength around 450 nm, so asto ensure that most or even all the light can pass through thecomposition or the polyimide. In addition, when the light emitted by theLED chip passes through the interface of two materials, the closer therefractive indexes of the two materials, the higher the light outputefficiency. In order to be close to the refractive index of the material(such as die bonding glue) contacting with the filament substrate (orbase layer), the organosilicon-modified polyimide composition has arefractive index of 1.4˜1.7, preferably 1.4˜1.55. In order to use theorganosilicon-modified polyimide resin composition as substrate in thefilament, the organosilicon-modified polyimide resin composition isrequired to have good light transmittance at the peak wavelength ofInGaN of the blue-excited white LED. In order to obtain a goodtransmittance, the raw materials for synthesizing theorganosilicon-modified polyimide, the thermal curing agent and the heatdispersing particles can be adjusted. Because the phosphor in theorganosilicon-modified polyimide resin composition may have certaineffect on the transmittance test, the organosilicon-modified polyimideresin composition used for the transmittance test does not comprisephosphor. Such an organosilicon-modified polyimide resin composition hasa transmittance of 86˜93%, preferably 88˜91%, or preferably 89˜92%, orpreferably 90˜93%.

In the reaction of anhydride and diamine to produce polyimide, theanhydride and the diamine may vary. In other words, the polyimidesproduced from different anhydrides and different diamines may havedifferent light transmittances. The aliphatic organosilicon-modifiedpolyimide resin composition comprises the aliphaticorganosilicon-modified polyimide and the thermal curing agent, while thefluorinated aromatic organosilicon-modified polyimide resin compositioncomprises the fluorinated aromatic organosilicon-modified polyimide andthe thermal curing agent. Since the aliphatic organosilicon-modifiedpolyimide has an alicyclic structure, the aliphaticorganosilicon-modified polyimide resin composition has a relatively highlight transmittance. In addition, the fluorinated aromatic,semi-aliphatic and full aliphatic polyimides all have good lighttransmittance in respect of the blue LED chips. The fluorinated aromaticorganosilicon-modified polyimide is synthesized from a siloxane-typediamine, an aromatic diamine comprising a fluoro (F) group (or referredto as fluorinated aromatic diamine) and an aromatic dianhydridecomprising a fluoro (F) group (or referred to as fluorinated aromaticanhydride). In other words, both Ar¹ and Ar² comprise a fluoro (F)group. The semi-aliphatic and full aliphatic organosilicon-modifiedpolyimides are synthesized from a dianhydride, a siloxane-type diamineand at least one diamine not comprising an aromatic structure (e.g. abenzene ring) (or referred to as aliphatic diamine), or from a diamine(one of the diamine is siloxane-type diamine) and at least onedianhydride not comprising an aromatic structure (e.g. a benzene ring)(or referred to as aliphatic anhydride). In other words, at least one ofAr¹ and Ar² has an alicyclic hydrocarbon structure.

Although blue LED chips have a main light-emitting wavelength of 450 nm,they may still emit a minor light having a shorter wavelength of around400 nm, due to the difference in the conditions during the manufactureof the chips and the effect of the environment. The fluorinatedaromatic, semi-aliphatic and full aliphatic polyimides have differentabsorptions to the light having a shorter wavelength of 400 nm. Thefluorinated aromatic polyimide has an absorbance of about 20% to thelight having a shorter wavelength of around 400 nm, i.e. the lighttransmittance of the light having a wavelength of 400 nm is about 80%after passing through the fluorinated aromatic polyimide. Thesemi-aliphatic and full aliphatic polyimides have even lower absorbanceto the light having a shorter wavelength of 400 nm than the fluorinatedaromatic polyimide, which is only 12%. Accordingly, in an embodiment, ifthe LED chips used in the LED filament have a uniform quality, and emitless blue light having a shorter wavelength, the fluorinated aromaticorganosilicon-modified polyimide may be used to produce the filamentsubstrate or the light-conversion layer. In another embodiment, if theLED chips used in the LED filament have different qualities, and emitmore blue light having a shorter wavelength, the semi-aliphatic or fullaliphatic organosilicon-modified polyimides may be used to produce thefilament substrate or the light-conversion layer.

Adding different thermal curing agents imposes different effects on thelight transmittance of the organosilicon-modified polyimide. Table 1-1shows the effect of the addition of different thermal curing agents onthe light transmittance of the full aliphatic organosilicon-modifiedpolyimide. At the main light-emitting wavelength of 450 nm for the blueLED chip, the addition of different thermal curing agents renders nosignificant difference to the light transmittance of the full aliphaticorganosilicon-modified polyimide; while at a short wavelength of 380 nm,the addition of different thermal curing agents does affect the lighttransmittance of the full aliphatic organosilicon-modified polyimide.The organosilicon-modified polyimide itself has a poorer transmittanceto the light having a short wavelength (380 nm) than to the light havinga long wavelength (450 nm). However, the extent of the difference varieswith the addition of different thermal curing agents. For example, whenthe thermal curing agent KF105 is added to the full aliphaticorganosilicon-modified polyimide, the extent of the reduction in thelight transmittance is less. In comparison, when the thermal curingagent 2021p is added to the full aliphatic organosilicon-modifiedpolyimide, the extent of the reduction in the light transmittance ismore. Accordingly, in an embodiment, if the LED chips used in the LEDfilament have a uniform quality, and emit less blue light having a shortwavelength, the thermal curing agent BPA or the thermal curing agent2021p may be added. In comparison, in an embodiment, if the LED chipsused in the LED filament have different qualities, and emit more bluelight having a short wavelength, the thermal curing agent KF105 may beused. Both Table 1-1 and Table 1-2 show the results obtained in thetransmittance test using Shimadzu UV-Vis Spectrometer UV-1800. The lighttransmittances at wavelengths 380 nm, 410 nm and 450 nm are tested basedon the light emission of white LEDs.

TABLE 1-1 Mechanical Thermal Curing Light Transmittance (%) StrengthOrganosilicon- Agent Film Tensile Modified Amount Thickness ElongationStrength Polyimides Types (%) 380 nm 410 nm 450 nm (μm) (%) (MPa) FullAliphatic BPA 8.0 87.1 89.1 90.6 44 24.4 10.5 Full Aliphatic X22-163 8.086.6 88.6 90.2 44 43.4 8.0 Full Aliphatic KF105 8.0 87.2 88.9 90.4 4472.6 7.1 Full Aliphatic EHPE3150 8.0 87.1 88.9 90.5 44 40.9 13.1 FullAliphatic 2021p 8.0 86.1 88.1 90.1 44 61.3 12.9

TABLE 1-2 Mechanical Thermal Curing Light Transmittance (%) StrengthOrganosilicon- Agent Film Tensile Modified Amount Thickness ElongationStrength Polyimides Types (%) 380 nm 410 nm 450 nm (μm) (%) (MPa) FullAliphatic BPA 4.0 86.2 88.4 89.7 44 22.5 9.8 Full Aliphatic 8.0 87.189.1 90.6 44 24.4 10.5 Full Aliphatic 12.0 87.3 88.9 90.5 44 20.1 9.0

Even when the same thermal curing agent is added, different added amountthereof will have different effects on the light transmittance. Table1-2 shows that when the added amount of the thermal curing agent BPA tothe full aliphatic organosilicon-modified polyimide is increased from 4%to 8%, the light transmittance increases. However, when the added amountis further increased to 12%, the light transmittance keeps almostconstant. It is shown that the light transmittance increases with theincrease of the added amount of the thermal curing agent, but after thelight transmittance increases to certain degree, adding more thermalcuring agent will have limited effect on the light transmittance.

Different heat dispersing particles would have different transmittances.If heat dispersing particles with low light transmittance or low lightreflection are used, the light transmittance of theorganosilicon-modified polyimide resin composition will be lower. Theheat dispersing particles in the organosilicon-modified polyimide resincomposition of the present disclosure are preferably selected to betransparent powders or particles with high light transmittance or highlight reflection. Since the soft filament for the LED is mainly for thelight emission, the filament substrate should have good lighttransmittance. In addition, when two or more types of heat dispersingparticles are mixed, particles with high light transmittance and thosewith low light transmittance can be used in combination, wherein theproportion of particles with high light transmittance is higher thanthat of particles with low light transmittance. In an embodiment, forexample, the weight ratio of particles with high light transmittance toparticles with low light transmittance is 3˜5:1.

Different siloxane content also affects the light transmittance. As canbe seen from Table 2, when the siloxane content is only 37 wt %, thelight transmittance is only 85%. When the siloxane content is increaseto above 45%, the light transmittance exceeds 94%.

TABLE 2 Elongation Organosilicon- Siloxane Thermal Tensile Elastic atResistance Modified Content Curing Tg Strength Modulus Break Chemical toPolyimide (wt %) Agent (° C.) (MPa) (GPa) (%) Transmittance ResistanceThermochromism 1 37 BPA 158 33.2 1.7 10 85 Δ 83 2 41 BPA 142 38.0 1.4 1292 ∘ 90 3 45 BPA 145 24.2 1.1 15 97 Δ 90 4 64 BPA 30 8.9 0.04 232 94 ∘92 5 73 BPA 0 1.8 0.001 291 96 ∘ 95

Heat Resistance

The factors affecting the heat resistance of the organosilicon-modifiedpolyimide resin composition include at least the type of the mainmaterial, the siloxane content, and the type and content of the modifier(thermal curing agent).

All the organosilicon-modified polyimide resin composition synthesizedfrom fluorinated aromatic, semi-aliphatic and, full aliphaticorganosilicon-modified polyimide have superior heat resistance, and aresuitable for producing the filament substrate or the light-conversionlayer. Detailed results from the accelerated heat resistance and agingtests (300° C.×1 hr) show that the fluorinated aromaticorganosilicon-modified polyimide has better heat resistance than thealiphatic organosilicon-modified polyimide. Accordingly, in anembodiment, if a high power, high brightness LED chip is used as the LEDfilament, the fluorinated aromatic organosilicon-modified polyimide maybe used to produce the filament substrate or the light-conversion layer.

The siloxane content in the organosilicon-modified polyimide will affectthe resistance to thermochromism of the organosilicon-modified polyimideresin composition. The resistance to thermochromism refers to thetransmittance determined at 460 nm after placing the sample at 200° C.for 24 hours. As can be seen from Table 2, when the siloxane content isonly 37 wt %, the light transmittance after 24 hours at 200° C. is only83%. As the siloxane content is increased, the light transmittance after24 hours at 200° C. increases gradually. When the siloxane content is 73wt %, the light transmittance after 24 hours at 200° C. is still as highas 95%. Accordingly, increasing the siloxane content can effectivelyincrease the resistance to thermochromism of the organosilicon-modifiedpolyimide.

Adding a thermal curing agent can lead to increased heat resistance andglass transition temperature. As shown in FIGS. 6, A1 and A2 representthe curves before and after adding the thermal curing agent,respectively; and the curves D1 and D2 represent the values afterdifferential computation on curves A1 and A2, respectively, representingthe extent of the change of curves A1 and A2. As can be seen from theanalysis results from TMA (thermomechanical analysis) shown in FIG. 6,the addition of the thermal curing agent leads to a trend that thethermal deformation slows down. Accordingly, adding a thermal curingagent can lead to increase of the heat resistance.

In the cross-linking reaction between the organosilicon-modifiedpolyimide and the thermal curing agent, the thermal curing agent shouldhave an organic group which is capable of reacting with the functionalgroup having active hydrogen in the polyimide. The amount and the typeof the thermal curing agent have certain effects on chromism, mechanicalproperty and refractive index of the substrate. Accordingly, a thermalcuring agent with good heat resistance and transmittance can beselected. Examples of the thermal curing agent include epoxy resin,isocyanate, bismaleimide, and bisoxazoline compounds. The epoxy resinmay be bisphenol A epoxy resin, such as BPA; or siloxane-type epoxyresin, such as KF105, X22-163, and X22-163A; or alicylic epoxy resin,such as 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate(2021P), EHPE3150, and EHPE3150CE. Through the bridging reaction by theepoxy resin, a three dimensional bridge structure is formed between theorganosilicon-modified polyimide and the epoxy resin, increasing thestructural strength of the adhesive itself. In an embodiment, the amountof the thermal curing agent may be determined according to the molaramount of the thermal curing agent reacting with the functional grouphaving active hydrogen in the organosilicon-modified polyimide. In anembodiment, the molar amount of the functional group having activehydrogen reacting with the thermal curing agent is equal to that of thethermal curing agent. For example, when the molar amount of thefunctional group having active hydrogen reacting with the thermal curingagent is 1 mol, the molar amount of the thermal curing agent is 1 mol.

Thermal Conductivity

The factors affecting the thermal conductivity of theorganosilicon-modified polyimide resin composition include at least thetype and content of the phosphor, the type and content of the heatdispersing particles and the addition and the type of the couplingagent. In addition, the particle size and the particle size distributionof the heat dispersing particles would also affect the thermalconductivity.

The organosilicon-modified polyimide resin composition may also comprisephosphor for obtaining the desired light-emitting properties. Thephosphor can convert the wavelength of the light emitted from thelight-emitting semiconductor. For example, yellow phosphor can convertblue light to yellow light, and red phosphor can convert blue light tored light. Examples of yellow phosphor include transparent phosphor suchas (Ba,Sr,Ca)₂SiO₄:Eu, and (Sr,Ba)₂ SiO₄:Eu(barium orthosilicate (BOS));silicate-type phosphor having a silicate structure such asY₃Al₅O₁₂:Ce(YAG(yttrium.aluminum.garnet):Ce), andTb₃Al₃O₁₂:Ce(YAG(terbium.aluminum.garnet):Ce); and oxynitride phosphorsuch as Ca-α-SiAlON. Examples of red phosphor include nitride phosphor,such as CaAlSiN₃:Eu, and CaSiN₂:Eu. Examples of green phosphor includerare earth-halide phosphor, and silicate phosphor. The ratio of thephosphor in the organosilicon-modified polyimide resin composition maybe determined arbitrarily according to the desired light-emittingproperty. In addition, since the phosphor have a thermal conductivitywhich is significantly higher than that of the organosilicon-modifiedpolyimide resin, the thermal conductivity of the organosilicon-modifiedpolyimide resin composition as a whole will increase as the ratio of thephosphor in the organosilicon-modified polyimide resin compositionincreases. Accordingly, in an embodiment, as long as the light-emittingproperty is fulfilled, the content of the phosphor can be suitablyincreased to increase the thermal conductivity of theorganosilicon-modified polyimide resin composition, which is beneficialto the heat dissipation of the filament substrate or thelight-conversion layer. Furthermore, when the organosilicon-modifiedpolyimide resin composition is used as the filament substrate, thecontent, shape and particle size of the phosphor in theorganosilicon-modified polyimide resin composition also have certaineffect on the mechanical property (such as the elastic modulus,elongation, tensile strength) and the warpage extent of the substrate.In order to render superior mechanical property and thermal conductivityas well as small warpage extent to the substrate, the phosphor includedin the organosilicon-modified polyimide resin composition areparticulate, and the shape thereof may be sphere, plate or needle,preferably sphere. The maximum average length of the phosphor (theaverage particle size when they are spherical) is above 0.1 μm,preferably over 1 μm, further preferably 1˜100 μm, and more preferably1˜50 μm. The content of phosphor is no less than 0.05 times, preferablyno less than 0.1 times, and no more than 8 times, preferably no morethan 7 times, the weight of the organosilicon-modified polyimide. Forexample, when the weight of the organosilicon-modified polyimide is 100parts in weight, the content of the phosphor is no less than 5 parts inweight, preferably no less than 10 parts in weight, and no more than 800parts in weight, preferably no more than 700 parts in weight. When thecontent of the phosphor in the organosilicon-modified polyimide resincomposition exceeds 800 parts in weight, the mechanical property of theorganosilicon-modified polyimide resin composition may not achieve thestrength as required for a filament substrate, resulting in the increaseof the defective rate of the product. In an embodiment, two kinds ofphosphor are added at the same time. For example, when red phosphor andgreen phosphor are added at the same time, the added ratio of redphosphor to green phosphor is 1:5˜8, preferably 1:6˜7. In anotherembodiment, red phosphor and yellow phosphor are added at the same time,wherein the added ratio of red phosphor to yellow phosphor is 1:5˜8,preferably 1:6˜7. In another embodiment, three or more kinds of phosphorare added at the same time.

The main purposes of adding the heat dispersing particles are toincrease the thermal conductivity of the organosilicon-modifiedpolyimide resin composition, to maintain the color temperature of thelight emission of the LED chip, and to prolong the service life of theLED chip. Examples of the heat dispersing particles include silica,alumina, magnesia, magnesium carbonate, aluminum nitride, boron nitrideand diamond. Considering the dispersity, silica, alumina or combinationthereof is preferably. The shape of the heat dispersing particles may besphere, block, etc., where the sphere shape encompasses shapes which aresimilar to sphere. In an embodiment, heat dispersing particles may be ina shape of sphere or non-sphere, to ensure the dispersity of the heatdispersing particles and the thermal conductivity of the substrate,wherein the added weight ratio of the spherical and non-spherical heatdispersing particles is 1:0.15˜0.35.

Table 3-1 shows the relationship between the content of the heatdispersing particles and the thermal conductivity of theorganosilicon-modified polyimide resin composition. As the content ofthe heat dispersing particles increases, the thermal conductivity of theorganosilicon-modified polyimide resin composition increases. However,when the content of the heat dispersing particles in theorganosilicon-modified polyimide resin composition exceeds 1200 parts inweight, the mechanical property of the organosilicon-modified polyimideresin composition may not achieve the strength as required for afilament substrate, resulting in the increase of the defective rate ofthe product. In an embodiment, high content of heat dispersing particleswith high light transmittance or high reflectivity (such as SiO₂, Al₂O₃)may be added, which, in addition to maintaining the transmittance of theorganosilicon-modified polyimide resin composition, increases the heatdissipation of the organosilicon-modified polyimide resin composition.The heat conductivities shown in Tables 3-1 and 3-2 were measured by athermal conductivity meter DRL-III manufactured by Xiangtan cityinstruments Co., Ltd. under the following test conditions: heatingtemperature: 90° C.; cooling temperature: 20° C.; load: 350N, aftercutting the resultant organosilicon-modified polyimide resin compositioninto test pieces having a film thickness of 300 μm and a diameter of 30mm.

TABLE 3-1 Weight Ratio [wt %] 0.0% 37.9% 59.8% 69.8% 77.6% 83.9% 89.0%Volume Ratio [vol %] 0.0% 15.0% 30.0% 40.0% 50.0% 60.0% 70.0% ThermalConductivity[W/m * K] 0.17 0.20 0.38 0.54 0.61 0.74 0.81

TABLE 3-2 Specification 1 2 3 4 5 6 7 Average Particle Size [μm] 2.7 6.6  9.0  9.6  13    4.1  12    Particle Size Distribution [μm] 1~7 1~201~30 0.2~30 0.2~110 0.1~20 0.1~100 Thermal Conductivity [W/m * K] 1.651.48 1.52 1.86 1.68 1.87 2.10

For the effects of the particle size and the particle size distributionof the heat dispersing particles on the thermal conductivity of theorganosilicon-modified polyimide resin composition, see both Table 3-2and FIG. 7. Table 3-2 and FIG. 7 show seven heat dispersing particleswith different specifications added into the organosilicon-modifiedpolyimide resin composition in the same ratio and their effects on thethermal conductivity. The particle size of the heat dispersing particlessuitable to be added to the organosilicon-modified polyimide resincomposition can be roughly classified as small particle size (less than1 μm), medium particle size (1-30 μm) and large particle size (above 30μm).

Comparing specifications 1, 2 and 3, wherein only heat dispersingparticles with medium particle size but different average particle sizesare added, when only heat dispersing particles with medium particle sizeare added, the average particle size of the heat dispersing particlesdoes not significantly affect the thermal conductivity of theorganosilicon-modified polyimide resin composition. Comparingspecifications 3 and 4, wherein the average particle sizes are similar,the specification 4 comprising small particle size and medium particlesize obviously exhibits higher thermal conductivity than specification 3comprising only medium particle size. Comparing specifications 4 and 6,which comprise heat dispersing particles with both small particle sizeand medium particle size, although the average particle sizes of theheat dispersing particles are different, they have no significant effecton the thermal conductivity of the organosilicon-modified polyimideresin composition. Comparing specifications 4 and 7, specification 7,which comprises heat dispersing particles with large particle size inaddition to small particle size and medium particle size, exhibits themost excellent thermal conductivity. Comparing specifications 5 and 7,which both comprise heat dispersing particles with large, medium andsmall particle sizes and have similar average particle sizes, thethermal conductivity of specification 7 is significant superior to thatof specification 5 due to the difference in the particle sizedistribution. See FIG. 7 for the particle size distribution ofspecification 7, the curve is smooth, and the difference in the slope issmall, showing that specification 7 not only comprises each particlesize, but also have moderate proportions of each particle size, and theparticle size is normally distributed. For example, the small particlesize represents about 10%, the medium particle size represents about60%, and the large particle size represents about 30%. In contrast, thecurve for specification 5 has two regions with large slopes, whichlocate in the region of particle size 1-2 μm and particle size 30-70 μm,respectively, indicating that most of the particle size in specification5 is distributed in particle size 1-2 μm and particle size 30-70 μm, andonly small amount of heat dispersing particles with particle size 3-20μm are present, i.e. exhibiting a two-sided distribution.

Accordingly, the extent of the particle size distribution of the heatdispersing particles affecting the thermal conductivity is greater thanthat of the average particle size of the heat dispersing particles. Whenlarge, medium and small particle sizes of the heat dispersing particlesare added, and the small particle size represents about 5-20%, themedium particle size represents about 50-70%, and large particle sizerepresents about 20-40%, the organosilicon-modified polyimide resin willhave optimum thermal conductivity. That is because when large, mediumand small particle sizes are present, there would be denser packing andcontacting each other of heat dispersing particles in a same volume, soas to form an effective heat dissipating route.

In an embodiment, for example, alumina with a particle size distributionof 0.1˜100 μm and an average particle size of 12 μm or with a particlesize distribution of 0.1˜20 μm and an average particle size of 4.1 μm isused, wherein the particle size distribution is the range of theparticle size of alumina. In another embodiment, considering thesmoothness of the substrate, the average particle size may be selectedas ⅕˜⅖, preferably ⅕˜⅓ of the thickness of the substrate. The amount ofthe heat dispersing particles may be 1˜12 times the weight (amount) ofthe organosilicon-modified polyimide. For example, if the amount of theorganosilicon-modified polyimide is 100 parts in weight, the amount ofthe heat dispersing particles may be 100˜1200 parts in weight,preferably 400˜900 parts in weight. Two different heat dispersingparticles such as silica and alumina may be added at the same time,wherein the weight ratio of alumina to silica may be 0.4˜25:1,preferably 1˜10:1.

In the synthesis of the organosilicon-modified polyimide resincomposition, a coupling agent such as a silicone coupling agent may beadded to improve the adhesion between the solid material (such as thephosphor and/or the heat dispersing particles) and the adhesive material(such as the organosilicon-modified polyimide), and to improve thedispersion uniformity of the whole solid materials, and to furtherimprove the heat dissipation and the mechanical strength of thelight-conversion layer. The coupling agent may also be titanate couplingagent, preferably epoxy titanate coupling agent. The amount of thecoupling agent is related to the amount of the heat dispersing particlesand the specific surface area thereof. The amount of the couplingagent=(the amount of the heat dispersing particles*the specific surfacearea of the heat dispersing particles)/the minimum coating area of thecoupling agent. For example, when an epoxy titanate coupling agent isused, the amount of the coupling agent=(the amount of the heatdispersing particles*the specific surface area of the heat dispersingparticles)/331.5.

In other specific embodiments of the present invention, in order tofurther improve the properties of the organosilicon-modified polyimideresin composition in the synthesis process, an additive such as adefoaming agent, a leveling agent or an adhesive may be selectivelyadded in the process of synthesizing the organosilicon-modifiedpolyimide resin composition, as long as it does not affect lightresistance, mechanical strength, heat resistance and chromism of theproduct. The defoaming agent is used to eliminate the foams produced inprinting, coating and curing. For example, acrylic acid or siliconesurfactants may be used as the defoaming agent. The leveling agent isused to eliminate the bumps in the film surface produced in printing andcoating. Specifically, adding preferably 0.01˜2 wt % of a surfactantcomponent can inhibit foams. The coating film can be smoothened by usingacrylic acid or silicone leveling agents, preferably non-ionicsurfactants free of ionic impurities. Examples of the adhesive includeimidazole compounds, thiazole compounds, triazole compounds,organoaluminum compounds, organotitanium compounds and silane couplingagents. Preferably, the amount of these additives is no more than 10% ofthe weight of the organosilicon-modified polyimide. When the mixedamount of the additive exceeds 10 wt %, the physical properties of theresultant coating film tend to decline, and it even leads todeterioration of the light resistance due to the presence of thevolatile components.

Mechanical Strength

The factors affecting the mechanical strength of theorganosilicon-modified polyimide resin composition include at least thetype of the main material, the siloxane content, the type of themodifier (thermal curing agent), the phosphor and the content of theheat dispersing particles.

Different organosilicon-modified polyimide resins have differentproperties. Table 4 lists the main properties of the fluorinatedaromatic, semi-aliphatic and full aliphatic organosilicon-modifiedpolyimide, respectively, with a siloxane content of about 45% (wt %).The fluorinated aromatic has the best resistance to thermo chromism. Thefull aliphatic has the best light transmittance. The fluorinatedaromatic has both high tensile strength and high elastic modulus. Theconditions for testing the mechanical strengths shown in Table 4˜6: theorganosilicon-modified polyimide resin composition has a thickness of 50μm and a width of 10 mm, and the tensile strength of the film isdetermined according to ISO527-3:1995 standard with a drawing speed of10 mm/min.

TABLE 4 Elongation Organosilicon- Siloxane Thermal Tensile Elastic atResistance Modified Content Curing Strength Modulus Break to Polyimide(wt %) Agent (MPa) (GPa) (%) Transmittance Thermochromism Fluorinated 44X22-163 22.4 1.0 83 96 95 Aromatic Semi-Aliphatic 44 X22-163 20.4 0.9 3096 91 Full Aliphatic 47 X22-163 19.8 0.8 14 98 88

TABLE 5 Addition Elongation Siloxane of Thermal Tensile Elastic atResistance Content Phosphor, Curing Tg Strength Modulus Break Chemicalto (wt %) Alumina Agent (° C.) (MPa) (GPa) (%) Transmittance ResistanceThermochromism 37 x BPA 158 33.2 1.7 10 85 Δ 83 37 ∘ BPA — 26.3 5.1 0.7— — — 41 x BPA 142 38.0 1.4 12 92 ∘ 90 41 ∘ BPA — 19.8 4.8 0.8 — — — 45x BPA 145 24.2 1.1 15 97 Δ 90 45 ∘ BPA — 21.5 4.2 0.9 — — — 64 x BPA  308.9 0.04 232 94 ∘ 92 64 ∘ BPA — 12.3 3.1 1.6 — — — 73 x BPA  0 1.8 0.001291 96 ∘ 95 73 ∘ BPA — 9.6 2.5 2 — — —

TABLE 6 Mechanical Thermal Curing Light Transmittance (%) StrengthOrganosilicon- Agent Film Tensile Modified Amount Thickness ElongationStrength Polyimides Types (%) 380 nm 410 nm 450 nm (μm) (%) (MPa) FullAliphatic BPA 8.0 87.1 89.1 90.6 44 24.4 10.5 Full Aliphatic X22-163 8.086.6 88.6 90.2 40 43.4 8.0 Full Aliphatic KF105 12.0 87.5 89.2 90.8 4380.8 7.5 Full Aliphatic EHPE3150 7.5 87.1 88.9 90.5 44 40.9 13.1 FullAliphatic 2021p 5.5 86.1 88.1 90.1 44 64.0 12.5

In the manufacture of the filament, the LED chip and the electrodes arefirst fixed on the filament substrate formed by theorganosilicon-modified polyimide resin composition with a die bondingglue, followed by a wiring procedure, in which electric connections areestablished between adjacent LED chips and between the LED chip and theelectrode with wires. To ensure the quality of die bonding and wiring,and to improve the product quality, the filament substrate should have acertain level of elastic modulus to resist the pressing force in the diebonding and wiring processes. Accordingly, the filament substrate shouldhave an elastic modulus more than 2.0 GPa, preferably 2˜6 GPa, morepreferably 4˜6 GPa. Table 5 shows the effects of different siloxanecontents and the presence of particles (phosphor and alumina) on theelastic modulus of the organosilicon-modified polyimide resincomposition. Where no fluorescent powder or alumina particle is added,the elastic modulus of the organosilicon-modified polyimide resincomposition is always less than 2.0 GPa, and as the siloxane contentincreases, the elastic modulus tends to decline, i.e. theorganosilicon-modified polyimide resin composition tends to soften.However, where phosphor and alumina particles are added, the elasticmodulus of the organosilicon-modified polyimide resin composition may besignificantly increased, and is always higher than 2.0 GPa. Accordingly,the increase in the siloxane content may lead to softening of theorganosilicon-modified polyimide resin composition, which isadvantageous for adding more fillers, such as more phosphor or heatdispersing particles. In order for the substrate to have superiorelastic modulus and thermal conductivity, appropriate particle sizedistribution and mixing ratio may be selected so that the averageparticle size is within the range from 0.1 μm to 100 μm or from 1 μm to50 μm.

In order for the LED filament to have good bending properties, thefilament substrate should have an elongation at break of more than 0.5%,preferably 1˜5%, most preferably 1.5˜5%. As shown in Table 5, where nofluorescent powder or alumina particle is added, theorganosilicon-modified polyimide resin composition has excellentelongation at break, and as the siloxane content increases, theelongation at break increases and the elastic modulus decreases, therebyreducing the occurrence of warpage. In contrast, where phosphor andalumina particles are added, the organosilicon-modified polyimide resincomposition exhibits decreased elongation at break and increased elasticmodulus, thereby increasing the occurrence of warpage.

By adding a thermal curing agent, not only the heat resistance and theglass transition temperature of the organosilicon-modified polyimideresin are increased, the mechanical properties, such as tensilestrength, elastic modulus and elongation at break, of theorganosilicon-modified polyimide are also increased. Adding differentthermal curing agents may lead to different levels of improvement. Table6 shows the tensile strength and the elongation at break of theorganosilicon-modified polyimide resin composition after the addition ofdifferent thermal curing agents. For the full aliphaticorganosilicon-modified polyimide, the addition of the thermal curingagent EHPE3150 leads to good tensile strength, while the addition of thethermal curing agent KF105 leads to good elongation.

TABLE 7 Specific Information of BPA Viscosity Content of EquivalentProduct at 25° C. Color Hydrolysable of Epoxy Hue Name (mPa · s) (G)Chlorine (mg/kg) (g/mol) APHA BPA 11000~15000 ≤1 ≤300 184~194 ≤30

TABLE 8 Specific Information of 2021P Viscosity Specific Melting BoilingWater Product at 25° C. Gravity Point Point Content Equivalent of HueName (mPa · s) (25/25° C.) (° C.) (° C./4 hPa) (%) Epoxy (g/mol) APHA2021P 250 1.17 −20 188 0.01 130 10

TABLE 9 Specific Information of EHPE3150 and EHPE3150CE Viscosity at 25°C. Softening Equivalent of Hue Product Name (mPa · s) Appearance PointEpoxy(g/mol) APHA EHPE3150 — Transparent 75 177 20 (in 25% Plate Solidacetone solution) EHPE3150CE 50,000 Light Yellow — 151 60 TransparentLiquid

TABLE 10 Specific Information of PAME, KF8010, X22-161A, X22-161B,NH15D, X22-163, X22-163A and KF-105 Viscosity Specific RefractiveEquivalent of Product at 25° C. Gravity Index at Functional Name (mm2/s)at 25° C. 25° C. Group PAME 4 0.90 1.448 130 g/mol KF8010 12 1.00 1.418430 g/mol X22-161A 25 0.97 1.411 800 g/mol X22-161B 55 0.97 1.408 1500g/mol NH15D 13 0.95 1.403 1.6~2.1 g/mmol X22-163 15 1.00 1.450 200 g/molX22-163A 30 0.98 1.413 1000 g/mol KF-105 15 0.99 1.422 490 g/mol

The organosilicon-modified polyimide resin composition of the presentembodiment may be used in a form of film or as a substrate together witha support to which it adheres. The film forming process comprises threesteps: (a) coating step: spreading the above organosilicon-modifiedpolyimide resin composition on a peelable body by coating to form afilm; (b) heating and drying step: heating and drying the film togetherwith the peelable body to remove the solvent from the film; and (c)peeling step: peeling the film from the peelable body after the dryingis completed to give the organosilicon-modified polyimide resincomposition in a form of film. The above peelable body may be acentrifugal film or other materials which do not undergo chemicalreaction with the organosilicon-modified polyimide resin composition,e.g., PET centrifugal film.

The organosilicon-modified polyimide resin composition may be adhered toa support to give an assembly film, which may be used as the substrate.The process of forming the assembly film comprises two steps: (a)coating step: spreading the above organosilicon-modified polyimide resincomposition on a support by coating to from an assembly film; and (b)heating and drying step: heating and drying the assembly film to removethe solvent from the film.

In the coating step, roll-to-roll coating devices such as roller coater,mold coating machine and blade coating machine, or simple coating meanssuch as printing, inkjeting, dispensing and spraying may be used.

The drying method in the above heating and drying step may be drying invacuum, drying by heating, or the like. The heating may be achieved by aheat source such as an electric heater or a heating media to produceheat energy and indirect convection, or by infrared heat radiationemitted from a heat source.

A film (composite film) with high thermal conductivity can be obtainedfrom the above organosilicon-modified polyimide resin composition bycoating and then drying and curing, so as to achieve any one orcombination of the following properties: superior light transmittance,chemical resistance, heat resistance, thermal conductivity, filmmechanical property and light resistance. The temperature and time inthe drying and curing step may be suitably selected according to thesolvent and the coated film thickness of the organosilicon-modifiedpolyimide resin composition. The weight change of theorganosilicon-modified polyimide resin composition before and after thedrying and curing as well as the change in the peaks in the IR spectrumrepresenting the functional groups in the thermal curing agent can beused to determine whether the drying and curing are completed. Forexample, when an epoxy resin is used as the thermal curing agent,whether the difference in the weight of the organosilicon-modifiedpolyimide resin composition before and after the drying and curing isequal to the weight of the added solvent as well as the increase ordecrease of the epoxy peak before and after the drying and curing areused to determine whether the drying and curing are completed.

In an embodiment, the amidation is carried out in a nitrogen atmosphere,or vacuum defoaming is employed in the synthesis of theorganosilicon-modified polyimide resin composition, or both, so that thevolume percentage of the cells in the organosilicon-modified polyimideresin composition composite film is 5˜20%, preferably 5˜10%. As shown inFIG. 8B, the organosilicon-modified polyimide resin compositioncomposite film is used as the substrate for the LED soft filament. Thesubstrate 420 b has an upper surface 420 b 1 and an opposite lowersurface 420 b 2. FIG. 8A shows the surface morphology of the substrateafter gold is scattered on the surface thereof as observed with vega3electron microscope from Tescan Corporation. As can be seen from FIG. 8Band the SEM image of the substrate surface shown in FIG. 8A, there is acell 4 d in the substrate, wherein the cell 4 d represents 5˜20% byvolume, preferably 5˜10% by volume, of the substrate 420 b, and thecross section of the cell 4 d is irregular. FIG. 8B shows thecross-sectional scheme of the substrate 420 b, wherein the dotted lineis the baseline. The upper surface 420 b 1 of the substrate comprises afirst area 4 a and a second area 4 b, wherein the second area 4 bcomprises a cell 4 d, and the first area 4 a has a surface roughnesswhich is less than that of the second area 4 b. The light emitted by theLED chip passes through the cell in the second area and is scattered, sothat the light emission is more uniform. The lower surface 420 b 2 ofthe substrate comprises a third area 4 c, which has a surface roughnesswhich is higher than that of the first area 4 a. When the LED chip ispositioned in the first area 4 a, the smoothness of the first area 4 ais favorable for subsequent bonding and wiring. When the LED chip ispositioned in the second area 4 b or the third area 4 c, the area ofcontact between the die bonding glue and substrate is large, whichimproves the bonding strength between the die bonding glue andsubstrate. Therefore, by positioning the LED chip on the upper surface420 b 1, bonding and wiring as well as the bonding strength between thedie bonding glue and substrate can be ensured at the same time. When theorganosilicon-modified polyimide resin composition is used as thesubstrate of the LED soft filament, the light emitted by the LED chip isscattered by the cell in the substrate, so that the light emission ismore uniform, and glare can be further improved at the same time. In anembodiment, the surface of the substrate 420 b may be treated with asilicone resin or a titanate coupling agent, preferably a silicone resincomprising methanol or a titanate coupling agent comprising methanol, ora silicone resin comprising isopropanol. The cross section of thetreated substrate is shown in FIG. 8C. The upper surface 420 b 1 of thesubstrate has relatively uniform surface roughness. The lower surface420 b 2 of the substrate comprises a third area 4 c and a fourth area 4e, wherein the third area 4 c has a surface roughness which is higherthan that of the fourth area 4 e. The surface roughness of the uppersurface 420 b 1 of the substrate may be equal to that of the fourth area4 e. The surface of the substrate 420 b may be treated so that amaterial with a high reactivity and a high strength can partially enterthe cell 4 d, so as to improve the strength of the substrate.

When the organosilicon-modified polyimide resin composition is preparedby vacuum defoaming, the vacuum used in the vacuum defoaming may be−0.5˜−0.09 MPa, preferably −0.2˜−0.09 MPa. When the total weight of theraw materials used in the preparation of the organosilicon-modifiedpolyimide resin composition is less than or equal to 250 g, therevolution speed is 1200˜2000 rpm, the rotation speed is 1200˜2000 rpm,and time for vacuum defoaming is 3˜8 min. This not only maintainscertain amount of cells in the film to improve the uniformity of lightemission, but also keeps good mechanical properties. The vacuum may besuitably adjusted according to the total weight of the raw materialsused in the preparation of the organosilicon-modified polyimide resincomposition. Normally, when the total weight is higher, the vacuum maybe reduced, while the stirring time and the stirring speed may besuitably increased.

According to the present disclosure, a resin having superiortransmittance, chemical resistance, resistance to thermochromism,thermal conductivity, film mechanical property and light resistance asrequired for a LED soft filament substrate can be obtained. In addition,a resin film having a high thermal conductivity can be formed by simplecoating methods such as printing, inkjeting, and dispensing.

When the organosilicon-modified polyimide resin composition compositefilm is used as the filament substrate (or base layer), the LED chip isa hexahedral luminous body. In the production of the LED filament, atleast two sides of the LED chip are coated by a top layer. When theprior art LED filament is lit up, non-uniform color temperatures in thetop layer and the base layer would occur, or the base layer would give agranular sense. Accordingly, as a filament substrate, the composite filmis required to have superior transparency. In other embodiments,sulfonyl group, non-coplanar structure, meta-substituted diamine, or thelike may be introduced into the backbone of the organosilicon-modifiedpolyimide to improve the transparency of the organosilicon-modifiedpolyimide resin composition. In addition, in order for the bulbemploying said filament to achieve omnidirectional illumination, thecomposite film as the substrate should have certain flexibility.Therefore, flexible structures such as ether (such as(4,4′-bis(4-amino-2-trifluoromethylphenoxy)diphenyl ether), carbonyl,methylene may be introduced into the backbone of theorganosilicon-modified polyimide. In other embodiments, a diamine ordianhydride comprising a pyridine ring may be employed, in which therigid structure of the pyridine ring can improve the mechanicalproperties of the composite film. Meanwhile, by using it together with astrong polar group such as —F, the composite film may have superiorlight transmittance. Examples of the anhydride comprising a pyridinering include2,6-bis(3′,4′-dicarboxyphenyl)-4-(3″,5″-bistrifluoromethylphenyl)pyridinedianhydride.

The LED filament structure in the aforementioned embodiments is mainlyapplicable to the LED light bulb product, so that the LED light bulb canachieve the omni-directional light illuminating effect through theflexible bending characteristics of the single LED filament. Thespecific embodiment in which the aforementioned LED filament applied tothe LED light bulb is further explained below.

Please refer to FIG. 9A. FIG. 9A illustrates a perspective view of anLED light bulb according to the third embodiment of the presentdisclosure. According to the third embodiment, the LED light bulb 20 ccomprises a lamp housing 12, a bulb base 16 connected with the lamphousing 12, two conductive supports 51 a, 51 b disposed in the lamphousing 12, a driving circuit 518 electrically connected with both theconductive supports 51 a, 51 b and the bulb base 16, a stem 19,supporting arms 15 and a single LED filament 100.

The lamp housing 12 is a material which is preferably light transmissiveor thermally conductive, such as, glass or plastic, but not limitedthereto. In implementation, the lamp housing 12 may be doped with agolden yellow material or its surface coated with a yellow film toabsorb a portion of the blue light emitted by the LED chip to reduce thecolor temperature of the light emitted by the LED light bulb 20 c. Inother embodiments of the present invention, the lamp housing 12 includesa layer of luminescent material (not shown), which may be formed on theinner surface or the outer surface of the lamp housing 12 according todesign requirements or process feasibility, or even integrated in thematerial of the lamp housing 12. The luminescent material layercomprises low reabsorption semiconductor nanocrystals (hereinafterreferred to as quantum dots), the quantum dots comprises a core, aprotective shell and a light absorbing shell, and the light absorbingshell is disposed between the core and the protective shell. The coreemits the emissive light with emission wavelength, and the lightabsorbing shell emits the excited light with excitation wavelength. Theemission wavelength is longer than the excitation wavelength, and theprotective shell provides the stability of the light.

The core is a semiconductor nanocrystalline material, typically thecombination of at least of one metal and at least one non-metal. Thecore is prepared by combining a coation precursor(s) with an anionprecursor(s). The metal for the core is most preferably selected fromZn, Cd, Hg, Ga, In, Ti, Pb or a rare earth. The non-metal is mostpreferably selected from O, S, Se, P, As or Te. The cationic precursorion may include all transition metals and rare earth elements, and theanionic precursor ions may be chosen from O, S, Se, Te, N, P, As, F, CL,and Br. Furthermore, cationic precursors may include elements orcompounds, such as elements, covalent compounds, or ionic compounds,including but are not limited to, oxides, hydroxides, coordinationcompounds, or metal salts, which serves as a source for theelectropositive element or elements in the resulting nanocrystal core orshell materials.

The cationic precursor solution may include a metal oxide, a metalhalide, a metal nitride, a metal ammonia complex, a metal amine, a metalamide, a metal imide, a metal carboxylate, a metal acetylacetonate, ametal dithiolate, a metal carbonyl, a metal cyanide, a metal isocyanide,a metal nitrile, a metal peroxide, a metal hydroxide, a metal hydride, ametal ether complex, a metal diether complex, a metal triether compound,a metal carbonate, a metal nitrate, a metal nitrite, a metal sulfate, ametal alkoxide, a metal siloxide, a metal thiolate, a metal dithiolate,a metal disulfide, a metal carbamate, a metal dialky carbamate, a metalpyridine complex, a metal dipyridine complex, a metal phenanthrolinecomplex, a metal terpyridine complex, a metal diamine complex, a metaltriamine complex, a metal diimine, a metal pyridine diimine, a metalpyrazollborate, a metal bis(pyrazole)borate, a metaltris(pyrazole)borate, a metal nitrosyl, a metal thiocarbamate, metaldiazabutadiene, a metal dithiocarbamate, a metal dialkylacetamide, ametal dialkylformamide, a metal formamidinate, a metal phosphinecomplex, a metal arsine complex, a metal diphosphine complex, a metaldiarsine complex, a metal oxalate, a metal imidazole, a metalpyrazolate, a metal Schiff base complex, a metal porphyrin, a metalphthalocyanine, a metal subphthalocyanine, a metal picolinate, a metalpiperidine complex, a metal pyrazolyl, a metal salicylaldehyde, a metalethylenediamine, a metal triflate compound or any combination thereof.Preferably, the cationic precursor solution may include a metal oxide, ametal carbonate, a metal bicarbonate, a metal sulfate, a metal sulfite,a metal phosphate, a metal phosphite, a metal halide, a metalcarboxylate, a metal hydroxide, a metal alkoxide, a metal thiolate, ametal amide, a metal imide, a metal alkyl, a metal aryl, a metalcoordination complex, a metal solvate, a metal salt or a combinationthereof. Most preferably, the cationic precursor is a metal oxide ormetal salt precursor and may be selected from zinc stearate, zincmyristate, zinc acetate, and manganese stearate.

Anionic precursors may also include elements, covalent compounds, orionic compounds, which are used as one or more electronegative elementsin the resulting nanocrystals. These definitions expect to be able toprepare ternary compounds, quaternary compounds and even more complexspecies using the methods disclosed in the present invention, in whichcase more than one cationic precursor and/or more than one anionprecursor can be used. When two or more cationic elements are usedduring a given monolayer growth, if the other part of thenanocrystalline contains only a single cationic, the resultingnanocrystals have a cationic alloy at the specified single layer. Thesame method can be used to prepare nanocrystals with anionic alloys.

The above method is applicable to the core/shell nanocrystals preparedusing a series of cationic precursor compounds of core and shellmaterials, for example, precursors of Group II metals (eg, Zn, Cd orHg), precursors of Group III metals (eg, Al, Ga or In), a precursor of aGroup IV metal (for example, Ge, Sn or Pb), or a transition metal (forexample, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc), Re, Fe, Ru, Os, Co,Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, etc.).

The components of the light absorbing shell may be the same or differentfrom the composition of the core. Typically, the light absorbing shellmaterial has the same lattice structure as the material selected for thecore. For example, if CdSe is used as the emission region material, theabsorption region material may be CdS. The light absorbing shellmaterial is chosen to provide good absorption characteristics and candepend on the light source. For example, CdS can be a good choice forthe absorption region when the excitation comes from a typical blue LED(within the wavelength range between 440 and 470 nm) solid stateillumination. For example, if the excitation originates from a purpleLED to produce a red LED by frequency down-conversion, then ZnSe orZnSe_(x)S_(1-x) (where x is greater than or equal to 0 and less than orequal to 1) is a preferred choice for the absorption region. As anotherexample, if one wishes to obtain near-infrared emission from a quantumdot for bio-medical applications (700-1000 nm) by using a red lightsource, then CdSe and InP often work as the absorption region material.

The protected area (wide bandgap semiconductor or insulator) at theoutermost outer shell of the quantum dot provides the desired chemicaland optical stability to the quantum dots. In general, a protectiveshell (also known as a protected area) neither effectively absorbs lightnor emits directional photons within the preferred excitation windowdescribed above. This is because it has a wide band gap. For example,ZnS and GaN are examples of protective shell materials. Metal oxides canalso be utilized. In certain embodiments, an organic polymer can be usedas a protective shell. The thickness of the protective shell istypically in the range between 1 and 20 monolayers. Moreover, thethickness can also be increased as needed, but this also increasesproduction costs.

A light absorbing shell includes a plurality of mono layers that form acompositional gradient. For example, the light absorbing shell caninclude three components varying in a ratio of 1:0:1 in a mono layerlocated closest to the core to a ratio 0:1:1 in a mono layer locatedclosest to the protective shell. By way of example, three usefulcomponents are Cd, Zn, and S and for instance, a mono layer closest tothe core may have a component CdS (ratio 1:0:1), a mono layer closest tothe protective shell may have a component corresponding to ZnS (Ratio0:1:1), and the intermediate mono layer between the core and theprotective shell may have a component corresponding to ZnSe_(x)S_(1-x)having a ratio (X):(1-X):1, and wherein X greater than or equal to 0 andless than or equal to 1. In this case, X is larger for a mono layercloser to the core than a mono layer that closer to the protectiveshell. In another embodiment, the transition shell consists of threecomponents, the ratio from the single layer closest to the core to thesingle layer closest to the protective shell: 0.9:0.1:1, 0.8:0.2:1,0.6:0.4:1, 0.4:0.6:1, and 0.2:0.8:1. Other combinations of Cd, Zn, S,and Se alloys can also be used as transition shells instead ofZnSe_(x)S_(1-x) as long as they have suitable lattice matchingparameters. In one embodiment, a suitable transition shell includes oneshell having Cd, Zn, and S components and the following layers listedfrom the layer closest to the light absorbing shell to the layer closestto the protective shell: Cd_(0.9)Zn_(0.1)S, Cd_(0.8)Zn_(0.2)S,Cd_(0.6)Zn_(0.4)S, Cd_(0.4)Zn_(0.6)S, Cd_(0.2)Zn_(0.8)S.

The LED filament 100 shown in FIG. 9A is bent to form a contourresembling to a circle while being observed from the top view of FIG.9A. According to the embodiment of FIG. 9A, the LED filament 100 is bentto form a wave shape from side view. The shape of the LED filament 100is novel and makes the illumination more uniform. In comparison with aLED bulb having multiple LED filaments, single LED filament 100 has lessconnecting spots. In implementation, single LED filament 100 has onlytwo connecting spots such that the probability of defect soldering ordefect mechanical pressing is decreased.

The stem 19 has a stand 19 a extending to the center of the bulb shell12. The stand 19 a supports the supporting arms 15. The first end ofeach of the supporting arms 15 is connected with the stand 19 a whilethe second end of each of the supporting arms 15 is connected with theLED filament 100.

Please refer to FIG. 9B which illustrates an enlarged cross-sectionalview of the dashed-line circle of FIG. 9A. The second end of each of thesupporting arms 15 has a clamping portion 15 a which clamps the body ofthe LED filament 100. The clamping portion 15 a may, but not limited to,clamp at either the wave crest or the wave trough. Alternatively, theclamping portion 15 a may clamp at the portion between the wave crestand the wave trough. The shape of the clamping portion 15 a may betightly fitted with the outer shape of the cross-section of the LEDfilament 100. The dimension of the inner shape (through hole) of theclamping portion 15 a may be a little bit smaller than the outer shapeof the cross-section of the LED filament 100. During manufacturingprocess, the LED filament 100 may be passed through the inner shape ofthe clamping portion 15 a to form a tight fit. Alternatively, theclamping portion 15 a may be formed by a bending process. Specifically,the LED filament 100 may be placed on the second end of the supportingarm 15 and a clamping tooling is used to bend the second end into theclamping portion to clamp the LED filament 100.

The supporting arms 15 may be, but not limited to, made of carbon steelspring to provide with adequate rigidity and flexibility so that theshock to the LED light bulb caused by external vibrations is absorbedand the LED filament 100 is not easily to be deformed. Since the stand19 a extending to the center of the bulb shell 12 and the supportingarms 15 are connected to a portion of the stand 19 a near the topthereof, the position of the LED filaments 100 is at the level close tothe center of the bulb shell 12. Accordingly, the illuminationcharacteristics of the LED light bulb 20 c are close to that of thetraditional light bulb including illumination brightness. Theillumination uniformity of LED light bulb 20 c is better. In theembodiment, at least a half of the LED filaments 100 is around a centeraxle of the LED light bulb 20 c. The center axle is coaxial with theaxle of the stand 19 a.

In the embodiment, the first end of the supporting arm 15 is connectedwith the stand 19 a of the stem 19. The clamping portion of the secondend of the supporting arm 15 is connected with the outer insulationsurface of the LED filaments 100 such that the supporting arms 15 arenot used as connections for electrical power transmission. In anembodiment where the stem 19 is made of glass, the stem 19 would not becracked or exploded because of the thermal expansion of the supportingarms 15 of the LED light bulb 20 c. Additionally, there may be no standin an LED light bulb. The supporting arm 15 may be fixed to the stem orthe bulb shell directly to eliminate the negative effect to illuminationcaused by the stand.

The supporting arm 15 is thus non-conductive to avoid a risk that theglass stem 19 may crack due to the thermal expansion and contraction ofthe metal filament in the supporting arm 15 under the circumstances thatthe supporting arm 15 is conductive and generates heat when currentpasses through the supporting arm 15.

In different embodiments, the second end of the supporting arm 15 may bedirectly inserted inside the LED filament 100 and become an auxiliarypiece in the LED filament 100, which can enhance the mechanical strengthof the LED filament 100. Relative embodiments are described later.

The inner shape (the hole shape) of the clamping portion 15 a fits theouter shape of the cross section of the LED filament 100; therefore,based upon a proper design, the cross section of the LED filament 100may be oriented to face towards a predetermined orientation. Forexample, as shown in FIG. 9B, the LED filament 100 comprises a top layer420 a, LED chips 104, and a base layer 420 b. The LED chips 104 arealigned in line along the axial direction (or an elongated direction) ofthe LED filament 100 and are disposed between the top layer 420 a andthe base layer 420 b. The top layer 420 a of the LED filament 100 isoriented to face towards ten o'clock in FIG. 9B. A lighting face of thewhole LED filament 100 may be oriented to face towards the sameorientation substantially to ensure that the lighting face of the LEDfilament 100 is visually identical. The LED filament 100 comprises amain lighting face Lm and a subordinate lighting face Ls correspondingto the LED chips. If the LED chips in the LED filament 100 are wirebonded and are aligned in line, a face of the top layer 420 a away fromthe base layer 420 b is the main lighting face Lm, and a face of thebase layer 420 b away from the top layer 420 a is the subordinatelighting face Ls. The main lighting face Lm and the subordinate lightingface Ls are opposite to each other. When the LED filament 100 emitslight, the main lighting face Lm is the face through which the largestamount of light rays passes, and the subordinate lighting face Ls is theface through which the second largest amount of light rays passes. Inthe embodiment, there is, but is not limited to, a conductive foil 530formed between the top layer 420 a and the base layer 420 b, which isutilized for electrical connection between the LED chips. In theembodiment, the LED filament 100 wriggles with twists and turns whilethe main lighting face Lm is always towards outside. That is to say, anyportion of the main lighting face Lm is towards the bulb shell 12 or thebulb base 16 and is away from the stem 19 at any angle, and thesubordinate lighting face Ls is always towards the stem 19 or towardsthe top of the stem 19 (the subordinate lighting face Ls is alwaystowards inside).

The LED filament 100 shown in FIG. 9A is curved to form a circular shapein a top view while the LED filament is curved to form a wave shape in aside view. The wave shaped structure is not only novel in appearance butalso guarantees that the LED filament 100 illuminates evenly. In themeantime, the single LED filament 100, comparing to multiple LEDfilaments, requires less joint points (e.g., pressing points, fusingpoints, or welding points) for being connected to the conductivesupports 51 a, 51 b. In practice, the single LED filament 100 (as shownin FIG. 9A) requires only two joint points respectively formed on thetwo conductive electrodes, which effectively lowers the risk of faultwelding and simplifies the process of connection comparing to themechanically connection in the tightly pressing manner.

Please refer to FIG. 9C. FIG. 9C is a projection of a top view of an LEDfilament of the LED light bulb 20 c of FIG. 9A. As shown in FIG. 9C, inan embodiment, the LED filament may be curved to form a wave shaperesembling to a circle observed in a top view to surround the center ofthe light bulb or the stem. In different embodiments, the LED filamentobserved in the top view can form a quasi-circle or a quasi U shape.

As shown in FIG. 9B and FIG. 9C, the LED filament 100 surrounds with thewave shape resembling to a circle and has a quasi-symmetric structure inthe top view, and the lighting face of the LED filament 100 is alsosymmetric, e.g., the main lighting face Lm in the top view may facesoutwardly; therefore, the LED filament 100 may generate an effect of anomnidirectional light due to a symmetry characteristic with respect tothe quasi-symmetric structure of the LED filament 100 and thearrangement of the lighting face of the LED filament 100 in the topview. Whereby, the LED light bulb 20 c as a whole may generate an effectof an omnidirectional light close to a 360 degrees illumination.Additionally, the two joint points may be close to each other such thatthe conductive supports 51 a, 51 b are substantially below the LEDfilament 100. Visually, the conductive supports 51 a, 51 b keeps a lowprofile and is integrated with the LED filament 100 to show an elegancecurvature.

Definition of the omni-directional light depends on regions and variesover time. Depending on different institutions and countries, LED lightbulbs which claim omni-directional light may need to meet differentstandards. For example, page 24 of the ENERGY STAR Program Requirementsfor Lamps (bulbs)—Eligibility Criteria Version 1.0 defines that anomnidirectional lamp in base-on position has to emit at least 5% oftotal flux (lm) in 135° to 180° zone, that 90% of measured intensityvalues may vary by no more than 25% from the average of all measuredvalues in all planes, and that luminous intensity (cd) is measuredwithin each vertical plane at a 5° vertical angle increment (maximum)from 0° to 135°. Japanese JEL 801 requires luminous flux of an LED lampwithin a 120 degrees zone about a light axis shall not be less than 70%of total flux. Because the above embodiment possesses a symmetricalarrangement of LED filament, an LED light bulb with the LED filament isable to meet various standards of omni-directional lamps.

Referring to FIGS. 10A to 10D, FIG. 10A is a perspective diagram of anLED light bulb 40 d according to an embodiment of the present invention,and FIGS. 10B to 31D are respectively side view, another side view, andtop view of the FIG. 10A. In the present embodiment, the LED light bulb40 d includes a lamp housing 12, a bulb base 16 connected to the lamphousing 12, a stem 19, a stand 19 a, and a single LED filament 100. TheLED filament 100 includes two conductive electrodes 110, 112 at twoends, a plurality of LED sections 102, 104 and a plurality of first andsecond conductive sections 130, 130′. Moreover, the LED light bulb 40 dand the single LED filament 100 disposed in the LED light bulb 40 d canrefer to related descriptions of the previous embodiments, wherein thesame or similar components and the connection relationship betweencomponents is no longer detailed.

As shown in FIG. 10A to FIG. 10D, the LED filament 100 comprises twofirst conductive sections 130 and one second conductive section 130′,and four LED sections 102, 104, and every two adjacent LED sections 102,104 are connected by the bending first or second conductive sections130, 130′. Therefore, the single LED filament 100 in the LED light bulb40 d can be bent severer because of the first and second conductivesections 130, 130′, and the curling change in bending is moresignificant. Moreover, the LED filament 100 can be defined as having aplurality of sections, each of the sections is connected between thefirst and second conductive sections 130, 130′, and each LED section102, 104 is formed into a respective section. In the present embodiment,the LED filament 100 is bent into four sections by two first conductivesections 130 and one second conductive sections 130′, wherein the fourLED sections 102, 104 are respectively the four sections.

Referring to FIG. 10A, FIG. 10B and FIG. 10C, in the present embodiment,the height of the upper two first conductive sections 130 may be greaterthan the height of the second conductive sections 130′ in the Zdirection. The height of the two LED sections 102, 104 is between theupper first conductive section 130 and the lower second conductivesection 130′ in the Z direction. The other two LED sections 102, 104extend downward from the corresponding first conductive section 130 inthe Z direction, and the height of the conductive electrodes 110, 112 isless than the height of the second conductive section 130′ in the Zdirection. As shown in FIG. 10C of the present embodiment, theprojections of the opposite LED sections 102, 104 are overlapped eachother when the LED filament 100 is projected on the XZ plane. In theembodiment as shown in FIG. 10D, when the LED filament 100 is projectedon the XY plane, all the projections of the first and second conductivesections 130, 130′ are located in one side of a straight line connectingbetween the conductive electrodes 110, 112.

Referring to FIGS. 11A to 11D, FIG. 11A is a perspective diagram of anLED light bulb 40 e according to an embodiment of the present invention,and FIGS. 11B to 11D are respectively side view, another side view, andtop view of the FIG. 11A. In the present embodiment, the LED light bulb40 e includes a lamp housing 12, a bulb base 16 connected to the lamphousing 12, a stem 19, a stand 19 a, and a single LED filament 100. TheLED filament 100 includes two conductive electrodes 110, 112 disposed attwo ends, a plurality of LED sections 102, 104 and a plurality of firstand second conductive sections 130, 130′. Moreover, the LED light bulb40 e and the single LED filament 100 disposed in the LED light bulb 40 ecan refer to related descriptions of the previous embodiments, whereinthe same or similar components and the connection relationship betweencomponents is no longer detailed.

As shown in FIG. 11A to FIG. 11D, the LED filament 100 comprises threefirst conductive sections 130 and two second conductive sections 130′,and six LED sections 102, 104, and every two adjacent LED sections 102,104 are connected by the bending first or second conductive sections130, 130′. Therefore, the single LED filament 100 in the LED light bulb40 e can be bent severer because of the first and second conductivesections 130, 130′, and the curling change in bending is moresignificant. Moreover, the LED filament 100 can be defined as having aplurality of sections, each of the sections is connected between thefirst and second conductive sections 130, 130′, and each LED section102, 104 is formed into a respective section. In the present embodiment,the LED filament 100 is bent into six sections by the three firstconductive sections 130 and the two second conductive sections 130′,wherein the six LED sections 102, 104 are respectively the six sections.

Referring to FIG. 11A, FIG. 11B and FIG. 11C, in the present embodiment,the height of the upper three first conductive sections 130 may begreater than the height of the lower two second conductive sections 130′in the Z direction. The height of the four LED sections 102, 104 isbetween the upper first conductive section 130 and the lower secondconductive section 130′ in the Z direction. The other two LED sections102, 104 extend downward from the corresponding first conductive section130 in the Z direction, and the height of the conductive electrodes 110,112 is less than the height of the first conductive section 130 in the Zdirection. As shown in FIG. 11C of the present embodiment, theprojections of the opposite LED sections 102, 104 are overlapped eachother when the LED filament 100 is projected on the XZ plane. In theembodiment as shown in FIG. 11D, when the LED filament 100 is projectedon the XY plane, the projections of the second conductive sections 130′are located in one side of a straight line connecting between theconductive electrodes 110, 112.

Referring to FIGS. 12A to 12D, FIG. 12A is a perspective diagram of anLED light bulb 40 f according to an embodiment of the present invention,and FIGS. 12B to 33D are respectively side view, another side view, andtop view of the FIG. 12A. In the present embodiment, the LED light bulb40 f includes a lamp housing 12, a bulb base 16 connected to the lamphousing 12, a stem 19, a stand 19 a, and a single LED filament 100. TheLED filament 100 includes two conductive electrodes 110, 112 disposed attwo ends, a plurality of LED sections 102, 104 and a plurality of firstand second conductive sections 130, 130′. Moreover, the LED light bulb40 f and the single LED filament 100 disposed in the LED light bulb 40 fcan refer to related descriptions of the previous embodiments, whereinthe same or similar components and the connection relationship betweencomponents is no longer detailed.

As shown in FIG. 12A to FIG. 12D, the LED filament 100 comprises threefirst conductive sections 130 and four second conductive sections 130′,and eight LED sections 102, 104, and every two adjacent LED sections102, 104 are connected by the bending first or second conductivesections 130, 130′. Therefore, the single LED filament 100 in the LEDlight bulb 40 f can be bent severer because of the first and secondconductive sections 130, 130′, and the curling change in bending is moresignificant. Moreover, the LED filament 100 can be defined as having aplurality of sections, each of the sections is connected between thefirst and second conductive sections 130, 130′, and each LED section102, 104 is formed into a respective sections. In the presentembodiment, the LED filament 100 is bent into eight sections by threeconductive sections 130 and four second conductive sections 130′,wherein the eight LED sections 102, 104 are respectively the eightsections.

Referring to FIG. 12A, FIG. 12B and FIG. 12C, in the present embodiment,the height of the upper three first conductive sections 130 may begreater than the height of the lower four second conductive sections130′ in the Z direction. The height of the six LED sections 102, 104 isbetween the upper first conductive section 130 and the lower secondconductive section 130′ in the Z direction. The other two LED sections102, 104 extend upward from the corresponding second conductive section130′ in the Z direction, and the height of the conductive electrodes110, 112 is approximately equal to the height of the upper secondconductive section 130′ in the Z direction. As shown in FIG. 12B andFIG. 12C of the present embodiment, the projections of the opposite LEDsections 102, 104 are overlapped each other when the LED filament 100 isprojected on the YZ plane (referring to FIG. 12B) or the XZ plane(referring to FIG. 12C). In the embodiment as shown in FIG. 12D, whenthe LED filament 100 is projected on the XY plane, all the projectionsof the first and second conductive sections 130, 130′ are located in oneside of a straight line connecting between the conductive electrodes110, 112.

Referring to FIGS. 13A to 13D, FIG. 13A is a perspective diagram of anLED light bulb 40 g according to an embodiment of the present invention,and FIGS. 13B to 34D are respectively side view, another side view, andtop view of the FIG. 13A. In the present embodiment, the LED light bulb40 g includes a lamp housing 12, a bulb base 16 connected to the lamphousing 12, a stem 19, a stand 19 a, and a single LED filament 100. TheLED filament 100 includes two conductive electrodes 110, 112 disposed attwo ends, a plurality of LED sections 102, 104 and a plurality of firstand second conductive sections 130, 130′. Moreover, the LED light bulb40 g and a single LED filament 100 disposed in the LED light bulb 40 gcan refer to related descriptions of the previous embodiments, whereinthe same or similar components and the connection relationship betweencomponents is no longer detailed.

As shown in FIG. 13A to FIG. 13D, the LED filament 100 comprises twoconductive sections 130, one second conductive section 130′, and fourLED sections 102, 104, and every two adjacent LED sections 102, 104 areconnected by the bending first and second conductive sections 130, 130′.Therefore, the single LED filament 100 in the LED light bulb 40 g can bebent severer because of the first and second conductive sections 130,130′, and the curling change in bending is more significant. Moreover,the LED filament 100 can be defined as having a plurality of sections,each of the sections is connected between the first and secondconductive sections 130, 130′, and each LED section 102, 104 is formedinto a respective section. In the present embodiment, the LED filament100 is bent into four sections by the two conductive sections 130 andthe one second conductive section 130′, wherein the four LED sections102, 104 are respectively the four sections.

Referring to FIG. 13A, FIG. 13B and FIG. 13C, in the present embodiment,the height of the upper two first conductive sections 130 may be greaterthan the height of the lower one second conductive sections 130′ in theZ direction. The height of the two LED sections 104 is between the upperfirst conductive section 130 and the lower second conductive section130′ in the Z direction. The other two LED sections 102, 104 extenddownward from the corresponding first conductive section 130 in the Zdirection, and the height of the conductive electrodes 110, 112 is lessthan the height of the second conductive section 130′ in the Zdirection.

In the present embodiment as shown in FIG. 13A, the LED filament 100extends around an axial direction and is resulted of a curling posturesimilar to spiral-like. As shown in FIG. 13B, the diameter of thespiral-like intermediate coil of the LED filament 100 (ie, the portionaround which the two LED sections 102, 104 are formed) is relativelysmall, and the diameter of the outer spiral-like coil of the LEDfilament 100 (ie, the portion of the other two LED sections 102, 104that extends outwardly and connects respectively with the conductiveelectrodes 110, 112) is relatively large. Moreover, the contour of theLED filament in the YZ plane may form a heart-like shape, and thedistance between the two first conductive sections 130 is less than thedistance between the two conductive electrodes 110, 112 in the Ydirection. In other embodiments, the distance between the two firstconductive sections 130 may be greater than or equal to the distancebetween the two conductive electrodes 110, 112 in the Y direction. Inthe present embodiment as shown in FIG. 13C, the LED filament 100 is ina shape like deformed S letter in the XZ plane. If the length of the LEDfilament 100 continues extending in a spiral-like posture along itsaxial direction, the curling posture of the LED filament 100 may have aplurality of overlapping shapes like deformed S letter in the XZ plane.In the present embodiment as shown in FIG. 13D, the curling posture ofthe LED filament 100 also has a shape like deformed S letter in the XYplane. If the length of the LED filament 100 continues extending in aspiral-like posture along its axial direction, the curling posture ofthe LED filament 100 may have a plurality of overlapping shapes likedeformed S letter in the XY plane. As shown in FIGS. 13C and 13D, in thepresent embodiment, the first and second conductive sections 130, 130′are located between the conductive electrodes 110, 112.

Referring to FIGS. 14A to 14D, FIG. 14A is a perspective diagram of anLED light bulb 40 h according to an embodiment of the present invention,and FIGS. 14B to 14D are respectively side view, another side view, andtop view of the FIG. 14A. In the present embodiment, the LED light bulb40 h includes a lamp housing 12, a bulb base 16 connected to the lamphousing 12, a stem 19, a stand 19 a, and a single LED filament 100. TheLED filament 100 includes two conductive electrodes 110, 112 at twoends, a plurality of LED sections 102, 104 and a single conductivesection 130. Moreover, the LED light bulb 40 h and the single LEDfilament 100 disposed in the LED light bulb 40 h can refer to relateddescriptions of the previous embodiments, wherein the same or similarcomponents and the connection relationship between components is nolonger detailed.

Referring to FIGS. 14A to 14D, in the present invention, the LEDfilament section 100 includes one conductive section 130, two LEDsections 102, 104, and between two adjacent LED sections 102, 104 isconnected by the conductive section 130. Wherein the LED filament 100having a circular arc at the highest point of the bending curvature,that is, each of the LED sections 102, 104 respectively having acircular arc at the highest point of the LED filament 100, and theconductive section also exhibits a circular arc at the low point of theLED filament. Moreover, the LED filament 100 can be defined as having aplurality of sections, each of the sections is connected between thefirst and second conductive sections 130, and each LED section 102, 104is formed into a respective section.

Moreover, since the LED filament 100 is equipped with a flexible baselayer, the flexible base layer preferably is made by anorganosilicon-modified polyimide resin composition, and thus the LEDsections 102, 104 themselves also have a certain degree of bendability.In the present embodiment, the two LED sections 102, 104 arerespectively bent to form in the shape like an inverted deformed Uletter, and the conductive section 130 is located between the two LEDsections 102, 104, and the degree of the bending of the conductivesection 130 is the same as or greater than the degree of the bending ofthe LED sections 102, 104. In other words, the two LED sections 102, 104of the LED filament are respectively bent at the high point to form inthe shape like an inverted deformed U letter and have a bending radiusvalue at R1, and the conductive section 130 is bent at a low point ofthe LED filament 100 and has a bending radius value at R2, wherein thevalue R1 is the same as or greater than the value R2. Through theconfiguration of the conductive section 130, the LED filament 100disposing in a limited space can be realized with a small radius bendingof the LED filament 100. In one embodiment, the bending points of theLED sections 102, 104 are at the same height in the Z direction.Further, in the Z direction, the stand 19 a of the present embodimenthas a lower position than the stand 19 a of the previous embodiment, andthe height of the present stand 19 a is corresponding to the height ofthe conductive section 130. For example, the lowest portion of theconductive section 130 can be connected to the top of the stand 19 a sothat the overall shape of the LED filament 100 is not easily deformed.In various embodiments, the conductive sections 130 may be connected tothe stand 19 a through the perforation of the top of the stand 19 a, orthe conductive sections 130 may be glued to the top of the stand 19 a toconnect with each other, but are not limited thereto. In an embodiment,the conductive section 130 and the stand 19 a may be connected by aguide wire, for example, a guide wire connected to the conductivesection 130 is drawn at the top of the stand 19 a.

As shown in FIG. 14B, in the present embodiment, the height of theconductive section 130 is higher than the two conductive electrodes 110,112 in the Z direction, and the two LED sections 102, 104 arerespectively shaped upward from the two conductive electrodes 110, 112to the highest point and then are bent down to connect with theconductive section 130. As shown in FIG. 14C, in the present embodiment,the contour of the LED filament 100 in the XZ plane is similar to the Vletter, that is, the two LED sections 102, 104 are respectively shapedobliquely upward and outward and are bent respectively at the highestpoint and then obliquely inwardly to connect with the conductive section130. As shown in FIG. 14D, in the present embodiment, the LED filament100 has a contour in the shape like S letter in the XY plane. As shownin FIG. 14B and FIG. 14D, in the present embodiment, the conductivesection 130 is located between the conductive electrodes 110, 112. Asshown in FIG. 14D, in the XY plane, the main bending points of the LEDsections 102, 104, and the conductive electrodes 110, 112 aresubstantially on the circumference centered on the conductive section130.

Referring to FIG. 15, which is a schematic diagram of the light emissionspectrum of an LED light bulb according to an embodiment of the presentinvention. In the present embodiment, the LED light bulb may be any ofthe LED light bulbs disclosed in the previous embodiments, and any oneof the LED light bulbs disclosed in the previous embodiments isprovided. The light emitted by the LED light bulb is measured by aspectrometer to obtain a spectrum diagram as shown in FIG. 15. From thespectrum diagram, the spectral distribution of the LED light bulb ismainly between the wavelength ranges of about 400 nm to 800 nm.Moreover, there are three peaks of intensity values P1, P2, P3 inwavelength ranges corresponding to the light emitted by the LED lightbulb. The wavelength of the intensity value P1 is between about 430 nmand 480 nm, the wavelength of the intensity value P2 is between about580 nm and 620 nm, and the wavelength of the intensity value P3 isbetween about 680 nm and 750 nm. The light intensity of the peak P1 isless than that of the peak P2, and the light intensity of the peak P2 isless than the light intensity of the peak P3. As shown in FIG. 15, sucha spectral distribution is close to the spectral distribution of aconventional incandescent filament lamp and also close to the spectraldistribution of natural light. In accordance with an embodiment of thepresent invention, a schematic diagram of the light emission spectrum ofa single LED filament is shown in FIG. 16. From the spectrum diagram, itcan be seen that the spectral distribution of the LED light bulb ismainly between the wavelength range of about 400 nm to 800 nm, and thereare three peaks of intensity values P1, P2, P3 in that wavelength range.The wavelength of the intensity value P1 is between about 430 nm and 480nm, the wavelength of the intensity value P2 is between about 480 nm and530 nm, and the wavelength of the intensity value peak P3 is betweenabout 630 nm and 680 nm. Such a spectral distribution is close to thespectral distribution of a conventional incandescent filament lamp andalso close to the spectral distribution of natural light.

The meaning of the term “a single LED filament” and “a single strip LEDfilament” as used in the present invention is mainly composed of theaforementioned conductive section, the LED section, the connectionbetween thereof, the light conversion layer (including the consecutivetop layer or the bottom layer, with continuous formation to cover orsupport all the components), and two conductive electrodes electricallyconnected to the conductive brackets of the LED light bulb disposing atboth ends of the LED filament, which is the single LED filamentstructure referred to in the present invention.

The various embodiments of the present invention described above may bearbitrarily combined and transformed without being mutually exclusive,and are not limited to a specific embodiment. For example, some featuresas described in the embodiment shown in FIG. C although not described inthe embodiment shown in FIG. A, those features may be included in theembodiment of FIG. A. That is, those skilled in the art can applies somefeatures of the FIG. A to the embodiment shown in the FIG. C withoutadditional creativity. Or alternatively, although the invention hasillustrated various creation schemes by taking the LED light bulb as anexample, it is obvious that these designs can be applied to other shapesor types of light bulb without additional creativity, such as LED candlebulbs, and the like.

The invention has been described above in terms of the embodiments, andit should be understood by those skilled in the art that the presentinvention is not intended to limit the scope of the invention. It shouldbe noted that variations and permutations equivalent to those of theembodiments are intended to be within the scope of the presentinvention. Therefore, the scope of the invention is defined by the scopeof the appended claims.

What is claimed is:
 1. An LED light bulb, consisting of: a lamp housingdoped with a golden yellow material or its surface coated with a yellowfilm; a bulb base connected to the lamp housing; a stem connected to thebulb base and located in the lamp housing, the stem comprises a standextending to the center of the lamp housing; a single flexible LEDfilament, disposed in the lamp housing, the flexible LED filamentcomprising: a plurality of LED sections, each of the LED sectionsincludes at least one LED chip; a plurality of conductive sections,located between the adjacent two LED sections, where each of theconductive sections includes a conductor, the conductor is copper foil;at least two conductive electrodes, respectively disposed correspondingto the LED sections and electrically connected to the LED sections; anda light conversion layer comprising a phosphor layer and a silicon layersuperposed on the phosphor layer, disposed on the LED chips and at leasttwo sides of the conductive electrodes, and a portion of the conductiveelectrodes is exposed by the light conversion layer, the LED chipcomprising a upper surface and a lower surface opposite to the uppersurface of the LED chip, wherein the phosphor layer directly contactsthe upper surface of the LED chip, and a base layer contacts the lowersurface of the LED chip; two conductive supports, each of the twoconductive supports connected with both the stem and the flexible LEDfilament; and a driving circuit, electrically connected with the twoconductive supports; a plurality of supporting arms, each of thesupporting arms comprise a first end and a second end opposite to thefirst end of the supporting arms, the first end of each of thesupporting arms is connected with the stand while the second end of eachof the supporting arms is connected with the flexible LED filament;wherein the base layer is formed from organosilicon-modified polyimideresin composition comprising an organosilicon-modified polyimide and athermal curing agent, wherein the organosilicon-modified polyimidecomprises a repeating unit represented by the following general Formula(I):

wherein Ar¹ is a tetra-valent organic group having a benzene ring or analicyclic hydrocarbon structure, Ar² is a di-valent organic group havinga monocyclic alicyclic hydrocarbon structure, R is each independentlymethyl or phenyl, n is 1˜5; wherein the organosilicon-modified polyimidehas a number average molecular weight of 5000˜100000; wherein thethermal curing agent is selected from the group consisting of epoxyresin, isocyanate and bisoxazoline compounds.
 2. The LED light bulbaccording to claim 1, wherein the thickness of the phosphor layer andthe silicon layer are equal.
 3. The LED light bulb according to claim 1,wherein the thickness of the phosphor layer and the silicon layer areunequal.
 4. The LED light bulb according to claim 3, wherein thethickness of the phosphor layer and the silicon layer respectively is 30to 70 um and 30 to 50 um.
 5. The LED light bulb according to claim 4,wherein the silicon layer does not contain phosphor.
 6. The LED lightbulb according to claim 5, wherein each of the LED sections includes atleast two LED chips that are electrically connected to each other. 7.The LED light bulb according to claim 6, wherein Ar¹ is derived from adianhydride, and Ar² is derived from a diamine.
 8. The LED light bulbaccording to claim 7, wherein Ar¹ is a tetra-valent organic group havinga monocyclic alicyclic hydrocarbon structure or a bridged-ring alicyclichydrocarbon structure, Ar² is a di-valent organic group comprising afunctional group having active hydrogen, where the functional grouphaving active hydrogen is any one of hydroxyl, amino, carboxy andmercapto.
 9. The LED light bulb according to claim 8, wherein theorganosilicon-modified polyimide resin composition further comprises anadditive selected from the group consisting of fluorescent powders, heatdispersing particles and a coupling agent.
 10. The LED light bulbaccording to claim 9, wherein the heat dispersing particles have aparticle size distribution of 0.1˜100 μm, the content of small particlesize of below 1 μm is 5˜20%, the content of medium particle size of 1˜30μm is 50˜70%, and the content of large particle size of above 30 μm is20˜40%.
 11. The LED light bulb according to claim 10, wherein thecontent of the fluorescent powders is no more than 7 times of the weightof the organosilicon-modified polyimide.
 12. The LED light bulbaccording to claim 11, wherein the base layer has an elongation at breakof 1˜5%, and a refractive index of 1.4˜1.55.
 13. The LED light bulbaccording to claim 12, wherein a spectral distribution of the light bulbis between wavelength range of about 400 nm to 800 nm, and three peakwavelengths P1, P2, P3 are appeared in the wavelength rangescorresponding to light emitted by the light bulb, the wavelength of thepeak P1 is between 430 nm and 480 nm, the wavelength of the peak P2 isbetween 580 nm and 620 nm, and the wavelength of the peak P3 is between680 nm and 750 nm, wherein a light intensity of the peak P1 is less thanthat of the peak P2, and the light intensity of the peak P2 is less thanthat of the peak P3.
 14. The LED light bulb according to claim 13,wherein points of the flexible LED filament in an xyz coordinates aredefined as X, Y, and Z, an x-y plane of the xyz coordinates isperpendicular to the height direction of the light bulb, a z-axis of xyzcoordinates is parallel with stem, where the conductive sectionscomprising first conductive sections and second conductive sections, andevery two adjacent LED sections are connected by the bending first andsecond conductive sections, and the number of the first conductivesections is one more than the number of the second conductive sections.15. The LED light bulb according to claim 14, wherein the flexible LEDfilament comprise three first conductive sections, two second conductivesection, and six LED sections and every two adjacent LED sections areconnected by the bending first and second conductive sections.
 16. TheLED light bulb according to claim 15, wherein the height of each of thethree first conductive sections is greater than the height of each ofthe two second conductive section in the Z direction.
 17. The LED lightbulb according to claim 16, wherein the height of each of the twoconductive electrodes is less than the height of each of the firstconductive section in the Z direction.
 18. The LED light bulb accordingto claim 17, wherein the projections of the opposite LED sections areoverlapped each other when the flexible LED filament is projected on theXZ plane.
 19. The LED light bulb according to claim 18, wherein when theflexible LED filament is projected on the XY plane, the projections ofthe second conductive sections are located in one side of a straightline connecting between the two conductive electrodes.
 20. The LED lightbulb according to claim 19, wherein when the flexible LED filament isprojected on the XY plane, the projections of a portion of the firstconductive sections are located in one side of a straight lineconnecting between the two conductive electrodes.